People who brush off their own ignorance or stupidity with flippancy.
I work with (way too many) people like this and it makes my shit itch when they make a brain-burningly stupid assertion or manage to completely mangle a common phrase in their own goddamn first language, you carefully put them right, taking care to be polite and not to be condescending... What do you get in response?
"Ehh, doesn't matter.", "lol, who cares?", "as if you even care about that, you dick?"
In the fucking sea, all of them.