Ever warned someone not to do something, and they didn't listen to you, and then they later paid the price for not heeding your warning? It can be a satisfying feeling—as long as the outcome isn't terrible and no one gets hurt.
1.) From Door-Dasher:
My 6 year old brother at the time was standing on the kitchen table with his socks on and it looked like he was about to jump off. I kid you not, before he jumped I literally said "don't jump off the table with socks on or you'll slip and break your arm." 5 seconds later he jumped off the table, his feet slipped out from under him, and he landed directly on his arm... breaking it.
2.) From SavageInkStudios: