Like others have said, be the bigger person and ignore it when possible, if their behaviour is too much then appologise to the group and leave. The worst thing you can do is get involved in some petty tit for tat, that just makes the whole experience miserable fo everyone else.

The worst I've had was some mid level dungeon, think it was Cutter's cry and a WHM was all over my ass the whole time, constantly berating me for not sleeping mobs (when I clearly was) and generally giving me a hard time, I ignored him for the most part but after a while I started to defend myself and to be fair to the tank so did he. WHM eventually left and we finished the dungeon with his replacement.