Off the top of my head:
Calexico (no stage presence whatsoever)
New Pornographers (dork music for dork people)
Belle and Sebastian (just way too fucking femme-y)_
the Decemberists (first time they were sort of ok, but by the second time, the novelty was gone, and they really blew)
Dean and Britta (lifeless victims of anorexia)
Bonnie Prince Billy (who let this guy out of his parent's basement?)
Common (actually, I can't think of a single rap show I've been to that didn't blow, I just need more than someone singing/rapping over prerecorded music to satisfy my LIVE music wants.)
Probably many more, I tend to forget the bad shows.