The confusing English language.. er, phrases.
You know when someone says something that someone doesn't believe or thinks is ridiculous or something, so then that person repeats what the other person has said and adds, "my ass!" to the end of it? Example: John says, "Malibu's Most Wanted is the best movie EVER!!" Jim replies, "Best movie ever, my ass!" OK. Why the "my ass?" I don't, for the life of me, get that. I mean I've definitely said it before, but I just realized today that I don't understand it at all.