What is the most drunk / stoned / otherwise incapacitated you've ever seen a performer?
Live, or on video.
I can't think of any live ones, but tonight I looked up Mixed Up Shook Up Girl and came across the below video.
Musically, it is superb, until Mr De Ville starts singing. The sideways sniffing, the vacant eyes... I seriously can't recall another performance where the singer is so obviously wacked off their dial. Does anyone else have some similarly bad examples?