My worst and best experience happened at the same time. I was playing a small gig and our singer used to keep a glass of water with cough drops melting in it on the stage at his feet. It's supposed to really help loosen the vocal cords but it also makes for a literal pain in the butt when you trip over it. I was goofing around making my way around the stage and stepped backwards onto the glass. Next thing i know i was on my back mid song. Rather then make it worst, I just finished the song laying on the floor but the crowd loved it. A few people thought that I was showing off and did it on purpose, little did they know I was limping around for the next few days.