Should co-author mention you in talk-abstract

Question

Simple question:

Suppose you have a joint work with another guy, and both of you agree that it is truly joint (i.e. both of you believe and agree there has been equally fundamental ideas for the papers from both sides, and also that there has been equal effort in realizing the project)

Now the guy does a presentation at a conference where in the abstract of the presentation he does not mention your name by the ritual ''this is joint work with...''. The organizer of the seminar is aware that it is joint and the abstract get modified after few days with your name.

Later on after few months, at another, way bigger conference, the guy does precisely the same thing (no mention to your name in the abstract), and there that is how the abstract passes.

My question: Is this considered an unethical behavior? In my position, would be the right thing to do to mail the coauthor to tell him that what he did is not acceptable?

Why do I find this puzzling: on one hand it just bothers me to see that someone who is presenting a work where I gave key ideas does not mention me at all in the abstract, since it feels wrong and pushy in a nasty sense. On the other I have the doubt that I might be over-reacting and that the etiquette does not banish such a behavior.

Fields of studies: math.

Edit: to make clearer the spirit of the question, from a comment below. In the top paragraph I mean that the two of us had a conversation and we agreed that the contribution to the paper in terms of ideas and practical effort in realizing the project is divided in equal parts. But then, asymmetrically, my name disappears when he gives talks on it. Therefore I cannot conclude that he does it because he believes that he has done more. So two options are left: 1) It is not part of the etiquette to write your co-author name in abstract of talks, so he just did not bother. 2) It is, but he did not do it because he wants to get more credit from people just looking at abstracts (is a big conference). So a positive answer to 1) would make not necessary the conclusion 2), which would be a relief, since 2) feels really nasty.

p.p.s: observe that the option 3) that one does not know that it is etiquette is excluded by the fact that many people actually write it in the abstract, the guy is aware of it, and therefore in the doubt it would be more convenient to choose the option without negative consequences. Therefore the omission can be only justified by the knowledge that it is not etiquette, that is 1).

Answer 1

I would say it's certainly inconsiderate, but I don't know if I'd go so far as to say "unethical", as long as you are credited in the talk itself.

Rather than telling your coauthor it's "unacceptable" to leave it out, he would be able to save face if you treat it as a simple oversight, whether or not you really believe that it is. (Even careful people make mistakes, and I am always in favor of applying Hanlon's razor.)

Hey, I saw your abstract for conference XXX. It looks like a very nice venue to discuss our work. One thing: it looks from the other abstracts like this conference follows the usual convention of mentioning coauthors in the abstract ("this is joint work with...") and it looks like this is missing from yours. If it isn't too much trouble, would you still be able to add it? I would really appreciate it.