Curbing misbehavior with public embarrassment. I had a lightbulb moment when I found out my pre-teens and teens were mortified if their old, slightly daft mom did something to embarrass them in front of strangers, friends, strange friends.... So if they get to acting a little too squirrelly, all I have to do is threaten to sing. Loudly. Show tunes. It only took two measures of "Oklahoma" in the middle of the frozen foods in WalMart to teach this simple lesson.
Caveat: this probably doesn't work on 3 year olds, as they will gladly belt out a song right along with you and possibly accompany the number with a dance routine.