Any band that gives a rubbish concert - particularly on purpose to be "cool" or because they get so off their face they can't see straight. I didn't mind so much when I was younger (it was part of the show watching the Happy Mondays), but I resent it now.
In fact disappointing live acts. The House of Love were awful once (being outshone by A House shows real commitment to doing a bad gig), as were Supergrass when I saw them in Amsterdam. They too were blown away by the support act, partly because they seemed desperate to play everything as loud as possible, and partly because the Presidents of the USA were just so much fun.