The Worst Error You've ever made reffing a game?

First 8th grade game: Team A scores a basket and forms up to press. B1 passes the ball along the endline to B2. This looks really weird. I call a violation and give the ball to Team A. At halftime I check my rulebook and right next to the rule is a red question mark I wrote down a few months earlier indicating I didn't understand what that rule meant. When I came out after halftime, Coach B was waiting for me. Holding a rulebook in his hand.

First varsity game: also my first three-man game, I had a block/charge play which I got right. I was so focused on making the right call that I forgot the number of the player who committed the foul. Reported the wrong number, won't do that again.