Jeez, awful songs? Too many to post.

But here's a stupid little one I taught my little niece to sing once, just to piss off my sister:

When it's bum-rubbin' time in the valley,
I rub my bum, then I come home to you.
You've been rubbin' your bum too
`Cause your fingers smell like poo
When it's bum-rubbin' time in the valley.

(sung to the tune of Red River Valley (more or less)