Jimi Hendrix at of all places Lincoln Center-1967 or 68 I think. He was 1/1/2 hours late, then announced he was "jamming tonite", proceeded to do interminable unbearably loud instrumental breaks. If you can believe it-a classical brass ensemble opened the concert, and to fill in some time Jimi Hendrix's drummer sat in with them. That was pretty awful also.The brass ensemble was fine by itself , but the audience was not the least appreciative. The next night I saw The Incredible String Band for the first time, became a big fan after I saw what could be done with acoustic instruments.
Next worse was The Grateful dead-early 70's. I saw them on the night Wes Montgomery-the jazz guitarist died. I guess they were doing some pseudo-rock jazz mostly instrumental and little recognizable material. You could tell the audience was not into it.