"The Joker" by Steve Miller Band takes the top spot for me. It was automatically awful the first time I heard it. It has only gotten worse since.
Otherwise, there are some songs that were okay at first, but have been hammered to the ground by stations that play older music, like Lynyrd Skynyrd's "Sweet Home Alabama", Don McClean's "American Pie", and Journey's "Don't Stop Believin'". They are songs that are considered so classic that everyone is supposed to love them, and they are played every five seconds, and I'm tired of them. But they aren't anywhere near the level of "The Joker"... As I said, that song is annoying just because it exists. It doesn't have to be played all of the time to be annoying, although it is very much played all of the time, too. >.>
As for modern music? I don't know... I'm not too familiar with it. Lol. I remember hating that song by Colbie Coillat(?), the name of which I forget... Fergie's "Big Girls Don't Cry", and more recently there's that song where this guy sings "Yeah, yeah, yeah". I remember seeing the title of the song and artist at one point, but I shoved it out of my mind because it was awful. To be fair, there aren't many modern pop songs I can tolerate anyway. Heck, there's not a lot of anything from the 80s and beyond that I can tolerate. xD