Why is menstruation funny?And then I watched the most recent episode of South Park, which was awesome.
Um...for the same reasons a lot of other stuff is funny.
It's a taboo subject - the shock of it all always gets a giggle right away and, immature or not, the gross-out factor is still fun. It's the new fart joke. You wait and see.
Here's a you tube link to the song at the end of the episode, since UK readers can't stream it, thanks to an irritating contract issue. I think, as usual, they've pretty much nailed it.