When it comes to slang, you should check 'Urban dictionary' http://www.urbandictionary.com/define.php?term=a%20can%20of%20whoopass I think it's ok to speak like that among friends ... for formal situations you should use a more correct english.

Wow, this one made my night. I sitting here looking at boring websites and then I see the pic of Spring with her post title about slang. And then I see her slang about whoop-ass and I thought I was going to bust a gut laughing! I've heard this slang often but I have to admit, only from a man. It is a bit vulgar. American English has some great slang, Spring, but I think you ought to give this one a pass (skip it, don't use it).

This expression is common enough to where I have hear it quite a bit (and I surround myself, Gena will be happy to know, with highly-educated, refined, and courteous individuals). This expression is almost always used in a light-hearted, joking manner, although it is very informal and should only be used with people you are familiar with. "To whoop somebody's ass" means to either to beat somebody physically or defeat them in a game or other activity. To "open a can of whoop-ass" is a playful way of saying you are going to beat the person, as though you could simply open a can and take it out. Like opening a can of beans.

No, this slang expression is not used often. I have never been around people who talk like that. It is crude and ugly language. A fine young lady like you would never want to talk like that, nor be around people who sound vulgar. Watch out what kind of slang expressions you learn.

Ha, ha. It's an American expression that Australians never use.