I cannot measure up to the insanity already posted above, but:
One of my first-ever top40 cover gigs. I was in over my head, and woefully underprepared, but just about able to pull it off.
Had an Electro2 for organs and clav, and the SY77 on top for a bunch of strings, brass, pianos, and synths, with the Rock & Pop expansion cards supplying a lot of the samples.
Sound check is all good.
Get up on stage for the gig, and I notice the first patch sounds really weird. Turns out the card slots had failed in the meantime. Okay. I figure Ill have to start playing and switch to alternative sounds on the fly if theyre missing sample elements.
Third song in, monitoring dies. Completely. For the rest of the show.
At some point, the panicked adrenaline gave way to hilarity over the realisation that not only could I not hear what I was playing, but I couldnt hear whether I was playing at all.
The singer hired me for another project a decade later though, so I must have come across okay...
By far the worst gig Ive ever played was two nights in a row at a notoriously raunchy carnival festival here in Northern Germany. The...it...there was this guy in the audience wearing a wig, a black corset which left his belly spilling out underneath, and blue nylon pantyhose in black stilettos, with nothing underneath... and that, while poignant, wasnt the worst thing about that job...nor was the Roman guard dry-humping the Greek flower girl against my Monitor the next night...nor the fact that I could hardly hear the drummer nor my own monitor over the accordion music and dance polka blaring at my side of the stage from one of the other stages some twenty yards away...