In reply to Timmd:
I think you need to have a certain level of intelligence, to "get" the joke, otherwise it's simply being nasty, uncaring, racist or crass.
I think you need to know your audience too.
If an outsider listened in to conversations with my mates, they'd get a very distorted picture of what we're really like, but because we know we don't believe what we're saying, it works fine, and is a good laugh too.
I just like laughing, it doesn't have to be me that's making people laugh (an ex GF thought it was a competition), but if your in company and everyone's laughing there's nothing better for the soul.