The worst act I ever saw was the third of three opening acts for Skinny Puppy at a Los Angeles show during their 2007 Mythrus tour. The band’s name was Silver Daggers, and they were some local synth–brass noise band.
Heckling started immediately into their set, and come song two, they were cranking knobs and doing what they could to hurt everyone’s ears, which only created more hecklers.
If I recall correctly, Silver Daggers never played their third song. Instead, their singer–keyboardist started crying and yelling at the audience, and before storming off stage, he threw his synth into the pit, hitting someone to my right. He also damaged some stage wiring, delaying Skinny Puppy’s start.
In any case, here’s the song Silver Daggers opened their set with: