In Am. English we say "ass". It's an idiomatic phrase because it doesn't mean to really kick someone in the butt / rear end. It means to punish. It's figurative speech. "You'd better finish that report by Friday, or the boss is going to kick your ass." The boss might yell and show his anger, but he won't really kick anybody. Some people, mostly young people I think, use it to say something is good, cool, etc. "This music really kicks ass" means they like the music. It can be an adjective, too. "That was a kick-ass party." Of course, the word ass is a bit strong and you shouldn't use it in a respectful / formal conversation. For this reason, some people were surprised when Obama used it in his interview. I don't know how strong "arse" is in other parts of the world.

No, it isn't. It was a response to the disaster in the Gulf. Maybe it was a warning. Or maybe he wanted to appear to be so tough to deal with that type of crises. Or maybe it was just a slip of the tongue... :)