For example, when discussing red-black trees in lecture, is it appropriate to use the phrase "Black Nodes Matter?"

The proof that red-black trees are balanced relies heavily on the property that each downward path originating from a node contains the same number of black nodes. Given this, I am wondering if it is appropriate to say #BlackNodesMatter.


10 Answers 10


This would be very unfortunate. People across the political spectrum have strong feelings about the words Black Lives Matter. Indeed, the subject matter of the movement is literally life and death. It's not something that should be made light of in mixed company, let alone in a classroom.

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    – ff524
    Commented Jul 17, 2016 at 16:29

The joke is in poor taste and inappropriate to a professional environment.

As pointed out by others, this might either be taken as moderate to serious offence in some places and just misunderstood in others, hence it is unlikely to achieve any of the intended effects. Places where most people would laugh wholeheartedly at the joke are probably places where I would not feel too comfortable staying.

While I agree that anything can theoretically be made light, this strongly depend on context and company.

As a general rule, if you feel like it is a good idea to check the appropriateness of a joke with somebody, then the joke is not appropriate.

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    +1, the last line is particularly important and worth noting.
    – jwg
    Commented Jul 15, 2016 at 10:01
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    @jwg Unfortunately that rule has a tendency toward "race to the bottom" type situations. Since by it's nature it moves the Overton Window every time someone uses it such that the line of acceptability can only ever move in one direction until we reach the point where the only possible humor that passes the test is the single joke "What's green and likes camping?""A boy sprout!"
    – Murphy
    Commented Jul 18, 2016 at 14:31
  • @Murphy this is not one of the things about which I am most worried.
    – jwg
    Commented Jul 18, 2016 at 15:06
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    @Murphy tbh that triggers me to no end fam. The rule works most of the time but not necessarily always. The gist is that if you feel something is wrong with your joke, then probably there is!
    – Three Diag
    Commented Jul 18, 2016 at 16:06

Besides for potentially offending your audience, a joke like the one you suggest can also detract from the goal of your presentation, which is presumably to inform or educate your audience.

For example, a couple of years ago I got this email, addressed to all of the authors on a paper I co-authored:

I wanted to write to say that I’m a big fan of your [REDACTED] work—it is a really cool idea that addresses a real problem, and it was great to see the work in this year’s [NAME OF CONFERENCE]. However, the actual talk as presented really bothered me, and I felt that it was important to write to you. Based on conversations during the breaks and at the end of the day, I know that I’m not the only person who feels this way.

The email went on to say that this person, and apparently others at the conference, thought a joke that was part of the talk (which was delivered by my co-author, and which I hadn't seen before) was sexist. Personally I thought the joke was more stupid than offensive, but I was unhappy with my co-author for using it - because when people talk about my paper during the breaks at a conference, I want them to be talking about the content of the work, not a joke that the presenter made. The joke was a distraction from the real goal of the talk.

Jokes are good when they support your goal of educating the audience, but not when they distract from that goal. (And definitely not when they're offensive.)

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    When in doubt, joke about pop culture (sports, films, etc), that can be funny and "connect" with students. Don't joke about things that are discriminatory, or involve harm or violation of rights. Putting that together and thinking back to FSU's old quarterback and typical jokes at many ACC/SEC schools: joke about James Winston and his crab legs theft, funny; joke about James Winston and his alleged rape, patently offensive) Commented Jul 14, 2016 at 23:16
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    I particularly liked this answer because of the concrete example of how something similar went horribly wrong. Commented Jul 15, 2016 at 18:41

Do not do this. Simply pointing out how nodes are identified as black, and relating it to Black Lives Matters, isn't a joke, it's a basic observation/wordplay. Race and color do not make good wordplay.

Are you African American? If not, don't relate the color of the nodes to someone else's race. In comedy this would be called punching down (a joke at the expense of groups with less power).

-Performing comedian for 6 years.

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    "Race and color do not make good wordplay." Pretty much the simplest way to explain the situation.
    – user18072
    Commented Jul 15, 2016 at 22:48
  • Thanks for the "punching down" term; I've needed that in the past. Commented Dec 25, 2016 at 14:25

The best you're going to get out of a classroom joke like this is a light chuckle.

The worst is that you've badly offended a student.

The risk:reward ratio is pretty heavily biased toward "Just don't."


I agree with many of the previous answers, and the major issue is that it can be offensive and distracting to poke fun at a sensitive and important topic. However, there are several other factors to keep in mind:

  1. Whatever you say may be overanalyzed. For example, in your red-black tree example, black nodes particularly matter since they play a special role in the proof. By contrast, "Black Lives Matter" means they matter as much as other lives (despite not being treated as being equally important), not that they matter more than others, so the analogy isn't very compelling. An uncharitable interpretation of your joke is that it's poking fun at or undermining BLM by comparing it to the assertion that black lives are unusually important relative to other lives. If that were the intent, it would make the joke (even) more offensive. Of course the purpose was presumably just to create a striking mnemonic, not to make a political statement, but when you joke about sensitive subjects you should expect to have far more read into your joke than you had intended.

  2. It's easy for the class to spin out of control. For example, a student may respond with "Don't red nodes matter too? I think the only fair statement is that all nodes matter." All that point, you really have no good response. It's not wise to go off topic into an actual political discussion, but you're in a messy situation since that response has emphasized your joke and made it even touchier politically (ending the discussion with "all nodes matter" would not be a good idea). If you get a follow up of this sort, I'd recommend apologizing for raising a sensitive issue and explaining that additional jokes and discussion are off topic. In any case, the point is that class members may take the joke further than you did and in a more explicitly political direction, and you shouldn't set up such a situation unless you are prepared to deal with it.

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    I appreciate the illustration in (2). re. "overanalyzed" part of the problem here is students usually assume the instructor is giving them relevant information they may use to understand the material. The more charitable students will try to draw analogies (informed by their worldviews) from the joke to the topic.
    – user18072
    Commented Jul 15, 2016 at 22:59

First I would like to mention that this specific joke would be very offensive to some people in the US and I think it is a very bad idea to use it.

However, to answer the question more generally, I think the appropriateness of joking about a charged subject in a lecture is very culture-dependent. In some countries, the worst-case scenario is that such a joke would be dismissed by some students as bad taste without any serious repercussions. However, in the US, I would personally either be extremely careful what I joke about or refrain from joking altogether, since there is a low threshold for what is considered offensive and repercussions can be very serious (just to be clear - I am not passing judgement on this). This is especially true if you are a non-native in the US, as you may not even be aware of what is considered offensive (I have seen this happen several times).

  • " In some countries, the worst-case scenario is that such a joke would be dismissed by some students as bad taste without any serious repercussions." Isn't that still bad? Especially if the students fail to process the material surrounding the poor-taste joke?
    – user18072
    Commented Jul 15, 2016 at 22:54
  • @djechlin that is worst-case. "Best" case i guess would be students finding it clever and as a result listening and studying better.
    – Bitwise
    Commented Jul 17, 2016 at 6:26
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    I guess I think if the worst case is that students dismiss the joke as i poor taste then you shouldn't tell the joke. If the best case is they somehow absorb the material very well, then you should use your excellent teaching skills to find some way to engage students that doesn't rely on bad taste.
    – user18072
    Commented Jul 17, 2016 at 21:37

Is the intention to provide an extra knowledge connection that would help students remember the material better? It seems like it could be helpful in that regard; that'd be a primary benefit ('pro').

Pros should be weighed against cons and the net compared to alternatives.

Are you demeaning the lives of people who are killed by police brutality, or the work of those advocating on their behalf, by calling attention to that movement in this setting? Based on the fact that you asked this question at all, it doesn't sound like you are intending to demean anyone, but whether or not people interpret it that way depends not only on intention but also on audience and context (e.g. classroom mood, what style students have come to expect from you), etc. If your audience receives a demeaning message from that line, that'd be a primary 'con.'

If you are supporting the work of those advocates by calling attention to their cause, as they seek, then your reference would be helping the #BlackLivesMatter movement (and whether this is a pro or con probably depends on how you feel about that movement).

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    There are almost certainly better ways to make a joke that provides an extra knowledge connection (e.g. make your own variation on this with your own punchline and an actual red-black tree). There are also much better ways to call attention to the movement. In weighing pros and cons, we should consider not only "is this good?" but also "is this the best way to achieve whatever I am trying to achieve?"
    – ff524
    Commented Jul 15, 2016 at 4:39
  • True, and not made sufficiently explicit in answer as originally posted. Clarified.
    – WBT
    Commented Jul 15, 2016 at 13:18
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    It's very clear to me the connection between "black nodes" and "black lives" is of no didactic value. No "pro" there. If the lecturer feels that #BlackLivesMatter needs to be brought up during this lecture, which is risky and not actually the subject of this question, this is not the right way to do that. Doesn't seem terribly enlightening to weigh "pros" and "cons" when there's one disputed pro against a glaringly obvious "you should not do this."
    – user18072
    Commented Jul 15, 2016 at 22:53
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    Attaching content lessons to common phrases that the audience is already very familiar with does help the lesson stick and make it easier to remember the material later on. I disagree with your absolutist statements.
    – WBT
    Commented Jul 16, 2016 at 2:59

Well, your question almost answers itself:

Is it appropriate to make a pun that references a highly charged topic in current events, in a lecture on an unrelated subject?

"Highly charged topic" perfectly matches racial slurs and sexist jokes. In particular "highly charged" implies several quite opposed sides with vested interest and emotions.

Which means that some people will likely get similarly offended like some would be with racials slurs or sexist jokes, and their offense is taken for the amusement values of others.

Is it appropriate? I think that answers itself. You probably wanted to rather ask whether it nets you sympathies. Maybe it will. But I'd recommend using more appropriate ways to do that.


It's very likely that if you make such a pun you make it a lot harder for the audience to reason rationally about the subject that you are talking about.

Half of your audience might spent 5 minutes thinking about the political implications of your statement instead of the math you are talking about.

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