I tell lots of jokes about things that disturb me - sexism, homophobia, racism, abuse, rape, genocide - because (and I've used other lame answers before - but this is the truest one) I feel that joking about them makes it easier for people to talk about it. Joking about it grants us power over it, and proves we are bigger.
Normally, in face to face interactions, I presume that the people around me (my friends - I'm less concerned with strangers) know I'm not sexist or homophobic. I even tend to do an overexaggerated male pig / hick voice when making these comments - which always struck me as a further sign of "I'm kidding."
Or have these topics overall become so taboo that suddenly any discussion of them that isn't dryly serious is a bad thing?
Caveat: I'd never try to force people to talk about something they aren't ready to talk about, and once I know a topic offends a friend, I try my best to leave it alone (though sometimes it comes back up.) I also don't whip these offensive jokes out the moment I meet somebody. I take the time to make sure that (in my opinion) they are able to deal with it.
I also rarely bring this side of my humor out online. For obvious reasons. (See Rule #4 on the rules for the community.)
So - what do people think?