I have a couple George Carlin albums and, also, Alvin and the Chipmunks Christmas Album (I never throw anything away).
Hoobastank's self-titled album. It's especially painful to listen to because I wasn't expecting much in the first place and somehow got much, much less.
I didn't read the whole thread, but here's mine ... It's the worst I ever bought, but I can't get rid of it because I'm stubborn ... Sugar Ray "Floored" which featured the hit single, "I just wanna fly." Decent song. The rest of the album sounds nothing like it. The worst part is, I was at a record store with some friends at the time of said purchase. I asked my friend Ed, who had that and Sublime's self-titled album, what he thought of each. He recommended Sugar Ray. After listening to the album, which blew sheep dingleberries, I asked him what the fuck he was thinking. His response: "You actually bought that piece of shit [Sugar Ray] album? You're an idiot!" But I keep it to remind myself not to buy crappy music.
I have a few: Someone gave me as a joke the Kay-Gees album, but I did not laugh once I played it. Just awful stuff. I ordered from Colombia House years ago a compilation of Smooth Grooves, supposed to be real artists singing their hip-hop and r&b tunes. Instead I got fake imitations that butchered songs I can't even bring myself to listen to anymore. Actually, I have a Club Latino and Bella Italo dance album that is utter crap. One piece of advice I give all of you, do not get sucked into ordering compilations from Colombia House because they are terrible and they will ruin any like you have for songs. This is why I stopped ordering things online.
The Doctor Detroit soundtrack. I have no idea what possessed me to purchase this... on an LP, no less.