That's a hard one, it's probably one that none of us know about, but if you want to know which band that is or was at least moderately popular is definitely bad, well, I honestly don't know. Linkin Park? I never liked them and genuinely think their sound was more noise than music. I know shit about music so I'm the least qualified to make such a statement, though.
I liked Linkin Park's first 2 albums, but man they sure did take a turn for the worse. Went from making nu metal to ultra poppy rock. Their alienation of their original fanbase was reflected in their sales too, dropped from 12x and 7x platinum on the first two down to 4x on the 3rd and then single platinum or below on every later album.
Can't say I agree on that one. While I'm not a fan of their creepy Texas Chainsaw Massacre looking masked personas, I enjoy a good many of their songs. Corey Taylor is a fantastic vocalist with a huge range and I enjoy his work in both Slipknot and Stone Sour. Not only do they have some good metal songs like Dead Memories and Vermillion Part 1, but they also have some great softer tracks like Snuff and Vermillion part 2.