Here are different ways of expressing your annoyance at someone or something. All of them make reference to the buttocks.
a pain in the ass - (You usually say this when you are angry.) When someone is a pain in the ass, you don't want to be around that person. If something is a pain in the ass, you don't want to do it.
a pain in the behind - (This usually means you're clearly annoyed, but you don't want to say "ass" because it's too vulgar.)
a pain in the you-know-what (You can also say this when you don't want to say "ass".)
a pain in the petoot (Petoot is a childish, funny way to call the buttocks)
1. I can't stand the new guy at work. He's such a pain in the ass; he's constantly complaining.
2. Tim tried to do his own taxes. He said it was such a pain in the you-know-what. Next year, he said he'll have an accountant do it for him.
3. Could you just follow instructions and quit being a pain in the behind? We're running late as it is.
Alright folks. Quit being a pain in the ass to your teachers. Do your homework; participate in class and of course, be respectful to your classmates.
the small guide