Following on from a (very late-to-the-party) discussion about this year's Glasto with some friends over dinner tonight, where we all decided Lauryn Hill was an absolute let down, who is the worst performer or group you've ever seen live? Especially thinking of people you really liked who let you down here, not just "was dragged to see Take That with DSis and they were shite" 
If you're not much of a music fan I suppose this stretches to comedians, actors, poets...anyone who gets up on stage and does a turn.