Paramecium

(You need a touch of background info for this one: I like the TV show Full House, and there is an episode where one character says to the other, "You have the attention span of a paramecium." There was more to it than that, but that's all that's necessary here. I thought i was funny, and started saying it when people did things that demonstrate lack of atten wait what was I talking about?
That sort of thing. Anyway, I had said it to Student A many times, and it had become a sort of inside joke. He had just done something else worthy of this phrase.)
Me: Student A, you have the attention span of a--
Student A: Paramecium, I know.
Me: Very good, Student A! You've learned how to insult yourself! Congratulations!
(Short pause while Student A ponders this possibility)
Student A: Oh Yeah? Well I bet I can insult myself better than you can!