I can't even think of where to start there are so many bad songs out there. A few that will send me into convulsions...

Criss Cross - Jump Around
Any song performed on South Park (particularly by Cartman)
Another vote for Seasons in the Sun
Aqua - Barbie Girl
ABBA - SOS (and most of the rest of their songs)
I Will Survive (Cake's version is terrible, the original is so much worse)
Anything from the movie Grease

EDIT: Forgot one, Vanilla Ice - Ice Ice Baby. I haven't heard that song in at least 10 years and the damn thing is stuck in my head just from typing out the name. Definitely the work of Satan.

-Mike