I used to be a woman who frowned on empty threats. I once heard of a woman who told her children that the oil spots in parking lots were actually the remains of children who didn't hold their parents' hands! I was horrified that anyone would inflict this Grimm-like story on their young children.
Then I had my own children. Two I handled pretty well. When we added our third one, though, my thinking changed one day at the grocery store. My daughters were four and six and their little brother was around six months old. The grocery store in our neighborhood had carts with little plastic cars in the front for children to ride in. Things started out fine, but then we left the produce section. The girls began frantically collecting coupons out of all those goofy machines that spit them out over, and over, and over. I used my best positive parenting techniques to encourage them to stay in the cart. It worked but they saw a loophole in my plan and climbed on top of the cart while grabbing can goods and laughing hysterically. In a moment of panic I sternly said, "The manager is coming. He does not allow for children to get of hand in his store."
Kiley and Laurel began looking around for the manager. Spotting an adult in a business suit they quickly sat down and behaved for the duration of our shopping. This worked for a few years with Spencer, too. Spencer often would ask me where the manager was - a sure clue that he was preparing for some stooge-like antics. Now that they're older they behave well when we're out (for the most part :)) I hope I haven't given my three kiddos an unnatural fear of persons in managerial positions.
So, what are some of the goofy things you tell your kids to encourage them to behave?