Definitely the worst was playing the Marina Theatre in Lowestoft when I was about 17.
My band had won a local talent show (£500, woo) and then got asked to play this showcase gig at the theatre with a bunch of other winners in different categories.
What we didn't know was we would be playing alongside the Miss Lowestoft Carnival Queen Competition! Not the most ideal pairing...heavy rock and a beauty contest!
The day went from bad to worse when our drummer announced he couldn't make it, so tried to contact a stand in but he didn't make it in time for the gig. We then had to wait backstage while the contest was going on for about four hours.
The event was supposed to have been built up to be this big spectacular that we would close with the curtain dropping to reveal us 'rocking out' with a full electric set but in reality what happened was the curtain opened to reveal my guitarist sitting on this massive stage, on the empty drum riser DI'd into the PA with a crap acoustic vainly attempting to turn it into an acoustic set with the singer. I didn't even get to play in the end, just sat there!
The place was deadly silent throughout and we received only polite applause at the end. At this point we got out of there as quickly as possible.
It was like a comedy sketch or something...looking back it's hilarious