Great thread. I have a few of my "favorites"; I don't claim their music sucks, but I personally just don't get it at all, and don't understand why they are as popular as they are. There are also entire genres that I cannot stand such as opera, indie rock, or country-western. Then there are sounds I don't even consider music such as techno, rap, and whatever they played at Sam Goody's I walked into last week; best I can describe it, it was a combination of bad disco music from the late '70s and the type of music Ace of Base was playing, whatever it was classified as. Doubtless, it was a top selling CD. Horrifying.
Here's my list, just off the top of my head:
1. Rolling Stones - a few good songs, majority just mediocre; never understood what made "Satisfaction" a rock'n'roll anthem.
2. Bob Dylan - how can anyone stand that nasal, whiny, screeching voice is a mystery to me.
3. Steely Dan - just sounds cheesy, song after song.
4. Radiohead - tried hard to get into their music, but just can't.
5. Greatful Dead - just so bland and boring; sounds like a dive bar music. Was it just the drug use that made them so popular until today? But why?
I will also admit that I'm surprised at some of the picks in this thread (Beatles, Pink Floyd, and Fleetwood Mac are the most surprising to me), but it just confirms how subjective and personal music tastes are. That said, there is music I don't get, and there is music that just plainly and objectively sucks, and to me shows lacks of refinement in someone's tastes. Easy listening, soft jazz, new age, almost all of best-selling music today to me is not even subject to a debate; it objectively blows, and I feel bad for those who can't hear it. It's like not being able to taste the difference between great Scotch and cheap Bourbon; you can't debate it.