Funniest thing I've seen:
A large, obviously accomplished lifter was front squatting a little over 400lbs for reps and a geeky, skinny kid goes up to him between sets and says, "Um, excuse me, but I think you're doing those wrong. The bar is supposed to be behind you." It felt rude to laugh but a few people did and he was blushing and confused. He learned what a front squat was that day though so all good.
Funniest thing I've done:
I'm sad to say this, but I've eatin' sh#* on the treadmill. I thought my foot was off the track but only made it half way on to the frame of the treadmill instead. My shoe caught the still running track at the toe, twisted my ankle inwards and down I went, first on to the treadmill and then the floor behind it as it spit me out in the clumsy trip of shame.