Christina Aguilara's Candyman. From all the things that were broadcasted 24/7, that must have been the most annoying song. That song is a very concentrated dose of agony, I tell you!
Of course there are tons of other vile popular songs, some even worse, but you didn't hear the most horrible ones as often.
I'd like to know what would happen if mainstream radio stations suddenly started playing something like Scar Symmetry rather often while saying "What an awesome tune" every time the song ends.
If the band would become famous and liked by the masses, I wouldn't know whether I'd laugh my ass off or would consider it as proof that the majority is lost.