Ever been in a store (say, Wal-Mart), watched a kid act up, and then had the parent say "if you don't stop, we're going home" (or some lame punishment like that)? The parent never follows through on their threat, and the kids learn the lesson "the parent never will".

If I'm in another aisle and hear this, I mouth off and say something like "yeah right, you're not going to do anything" in response to the parent's threat. I say it loud enough so that the parent can hear it. Hehe fun to watch the results!