Nickelback, Fallout Boy, Metallica (and all the other hair metal bands),Limp Bizkit,
Creed, Black Eyed Peas, Milli Vanilli (I need a memory erasure to forget them),
Status Quo (only they can play just one song with many different titles),
Nelly Furtado/Lindsay Lohan/Beyonce/Britney/Christina/Jessica&Ashlee Simpson clan.

It can't get much worse...

Oh yes it can. The very worst never even gets a mention. One of my friends from long ago, played in a band and had played with the Triffids, was most offended when I congratulated him and the band on their innovative polyrythmic score. The thing was they were (or thought they were) in synch, Oh dear, Good and Bad. The worst concert was (can't even remember the name now played after a lot of hype, maybe one track was something about a fox? Horrendous) ( Later another very obscure, but very interesting, eastern band I did some PC work for (seemed to get a lot of musos to work for as the IT tecnology became affordable and a home studio easy and I kindof have a background in that scene) did the polyrythimc thing deliberately, and very well. Might have a CD stored away somewhere. )

Right. I knew I forgot something. I should have included Glass Candy to my list.
I haven't heard such terrible sound for ages.

That reminds me of the worst line in a song, "You can't touch this".
Fortunately, MC Hammer is no longer around.