What grammar or vocabulary mistakes do people make that you find amusing rather than annoying?
I find when people use "literally" when they really mean figuratively to can lead to some rather amusing mental images.
Also when someone ends a sentence by saying "period" to emphasise a point but sometimes they are yelling the statement so it really should end with an exclamation point. It's even better when someone is typing it out, for example "That's the worst drink ever period!" would really be "That's the worst drink ever.!" So I imagine them saying the sentence calmly then screaming "AGH!" after a pause.
I guess if you can discuss your actual pet peeves too if you want, GO!