Not a gig exactly, but
I did a variety show once where, after a particular song, the music was supposed to stop and the director come on stage to do some speech or another. The music stopped and the director walked on. The musical director however had forgotten about the speech and launched straight into the next song, leaving the director no choice but to walk straight back off the stage again.
(Inflatable Giraffe Punctureless since 1985, Mon 29 Jul 2013, 12:35, Reply)