Find a guy who likes to do this type of stuff. When you grab his leg, when that leg gets really heavy then let it slip from your hands. He'll fall to the ground like a sack of bricks. His attempt will fail, and you'll get some giggles when you see how hard he hits the ground lol. That technique requires you to hold his leg. When you let go, he won't have anything to support his escape flip. he will fall into emptiness.So this is the example i would use.
Here is a quite simply ridiculous martial arts move. That I don't understand and I can't do and I am not a pro MMA fighter.
Sometimes it's better to let go. I've seen this happen to someone in class. The person didn't mean to let go. He just had a weak grip that couldn't support that weight so as soon as the leg got heavy, the person trying to escape lost the support that he needed. He hit the ground and busted up his knees a little, (we train on concrete).