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

[OKREF]

This summer at camp, biggest brain fart I've ever had. 3 man mechanics. Free throw late in the game. Shooting team down 1, under 20 seconds left, second free throw. Shooter shoots the shot, runs about five feet in before the shot hits the rim. Makes the shot. I step in call a violation and wave off the bucket. Only problem is I was in the trail position. The "C" said he just missed it. It was so egregious, I just saw it and reacted.