I have a new funniest moment, just happened yesterday.
A guy (probably in his 40's, looked big but didn't have great form) was doing lateral raises with a pretty light weight (about 15lbs) but he was doing it the way where he bends over a fair way and has his elbows bent a lot. And he had terrible technique, and towards the end of his set, he was throwing his entire torso back and jerking the weight up.... then I just glanced over when I'd sat up from my bench, and saw the weight fly out of his left hand and smash a mirror.
The whole mirror smashed, although the shards didn't fall because of some safety film stuff. It was pretty funny anyway.
Some guys just go a little bit crazy trying to get a few more reps. I think if you can't get the weight up with proper form, you've done your job and the set is over.