A word like ret*d is funny in certain contexts, but in a very lowbrow way. Jokes like this, ie. penis jokes, fart jokes, fat jokes, racial jokes, get old really fast. Given the context, almost anything is funny. If you're going to offend one group, you must also offend every other group to avoid getting criticized, a la South Park.
Yes, I know it's weird logic, but it does seem to hold.