I agree that you're over-reacting, and I think once you take it a bit easier you'll see for yourself what's wrong here.

It's definitely *not* professional to prepare your defence before you even know what you're accused of. Just because you have an award, and almost all your students like you, doesn't prove you're infallible and doesn't prove you didn't do this one thing wrong that's been complained about. You're not accused of *always* being wrong or of being a certain kind of person, you're accused of *one incident*. If you act as though your general good character proves you innocent of a single incident, then you would be presenting yourself as arrogant, entitled and, frankly, clueless.

So don't go in with the attitude that "I don't know what it is you think I did wrong, but I've never done anything wrong in my life and I can prove that because most people like me".

Instead, listen to the complaint. It's possible the incident is *completely* invented (in which case perhaps you can call *specific* witnesses who were present in the same class it was alleged to happen, rather than *general* testimony that you're a good teacher). It might be that something happened that you thought at the time was fine (perhaps even still think is fine) but the student didn't like, in which case you can probably apologise, learn the lesson that not everyone likes it, and move on. That is the professional thing to do, but unfortunately you can't start doing it until you know the details, and you don't know the details yet.

For example, if your "friendly and approachable" style includes a certain amount of joking around, you have to be prepared for the possibility that not everyone likes being joked around, and it's possible that you did mock something they did or said. That would be fine if they thought it was funny, not so much if they didn't, which is out of your control. And just because someone laughs at the time doesn't mean they really enjoyed it -- people try to cover embarrassment or discomfort. So having separate feedback outside the class is helpful to you, to learn things you otherwise can't, it's just a shame that it's coming in the form of a complaint.

If you go in assuming you did some small thing wrong, you'll be pleasantly surprised if you didn't, or if you did but you can make amends. If you go in assuming that a person with good teaching evaluations cannot possibly have done anything wrong, then you'll get a nasty shock.

> even more hurtful is that my colleagues might start viewing me as a
> cruel person who mocks the weaker students.

That would be bad, but it's unlikely that a single minor incident, handled in confidence and settled to the satisfaction of whoever is in charge, will get you that reputation. And it'd still better than them viewing you as a cruel person who mocks the weak, refuses to accept even the possibility of being wrong, and keeps their exhaustive defence argument ready to go at a moment's notice.

Don't let your (natural, understandable) worry over the accusation, turn you into an even worse person than what you're worried you might be accused of.