Humor has no forbidden themes. Forbidding themes approachable in humour is a slippery slope we, as a society, should not wish to enter.

Uncomfortable themes that have been used in humour: death? Check. Religion? There's a whole subculture of it. Torture? Check. Disabilities? Of course. Dim-witts? Oh boy has it been used. War? The more war there is, the more it's mocked.

Why should rape be any different?