Idiots in general
When I was in 6th form a few idiots started throwing grapes at me and my friends, I mutter
"Oh, talk about mature" to which one of my friends replied "Yeah, but we were playing with a transformer earlier" (Another of my friends had shown us a transformer figure he had in his bag). I then spent the next few minutes trying to explain why it was different, only to have him say "Yeah, whatever" and turn away.
Another thing is my voice. People seem to think it's hilarious to mock my voice because it sounds different, and it never seems to occur to them why my voice actually sounds the way it does. One time it was actually one of my friends (we were "joking" around pretending to be each other) imitating my voice which actually shocked me so much that I recorded my voice later that day and listened to it because I'd thought it had changed, but it hadn't.