I'm not sure I could without repeating myself, and besides a lot of things I dislike intensely, other folks respond to well. Also, I'm unsure which of these have been discussed here, already:
Like I said in the Reboot thread, the Loeb, Kelly, and (to a degree) Puckett Supergirl runs are awful.
I've said before I really hated Identity Crisis, but I re-read it, and even though I do still hate it, it's got a lot of weirdly well-done scenes. If you don't mind a really badly constructed mystery or the breaking of cute and beloved characters, there's a lot to recommend it, I guess, although in good conscience I can't.
Crisis on Infinite Earths is really, really bad. Despite a master on art duties, even the pages themselves aren't very pretty to look at. This is one of those things that maybe you had to be there for. I'd suggest just ignoring it.
Anything drawn by Greg Land or Ed Benes.