I don't know why, but I looked up the word ass in my English usage dictionary. I know it's totally childish, but I found it hilarious.

An ass is an animal which is related to a horse but which is smaller and has long ears.

If you describe someone as an ass, you think that they are silly or that they do silly things.

Your ass is your bottom. (Very Rude, Informal) (In Britain use arse or bum)

To kick ass or to kick someone's ass means to show them that you are angry with them, either by telling them or by using physical force.

Saying that someone can kiss your ass is a very rude way of expressing anger or disagreement.

If you say that someone makes an ass of themselves, you mean they behave in a way that you think is very silly.