I saw this on boingboing earlier today. It's one of those things that will make some people crack up, and make most people look at those people who are cracking up with confusion and fear.
For some reason, xkcd hasn't been on my radar until today, which is a shame because the artist has some really funny, thoughtful, and insightful cartoons. But it's in bloglines now, for sure.
If you think this comic is as funny as I do, you can buy it on a T-shirt. Sweet.