Oh, let's list a few, shall we?
When people are hypocrites.
When people think that they are better than someone else.
When children are rude to adults.
When boys are rude to girls.
When you ask someone to stop doing something, and their response is "Deal with it." (Seriously, by asking you to stop, I am dealing with it.)
When people take a REALLY REALLY BAD situation and try to find a good thing. (Earlier this year, a boy in my class died of cancer, so a teacher gave us a day for grief, and one girl's response was "Yay, no test.")
When there is a circle of people talking, and someone stands right in the middle.
When someone eats all but a bite of a package of food, and then puts it back.
I think I'll stop there, because this list could go on forever.