"Stuck on a Lamp Post Prank" shows how if you wrap someone's legs around a lamppost and have them sit down cross-legged, it's nearly impossible to get back up without help.

It's actually a restraint technique they used in World War Two. Unless you have massive upper body strength, you can't lift yourself up high enough to unlock your legs.

If you try it on your friend, don't leave them there, because they'll die if you do. After about 10 minutes, you start cramping up and pass out. Then when you fall backward, it puts all the pressure on your ribcage, and you stop breathing.

After a while in this position, 10 to 15 minutes, you start getting cramps in your legs, which becomes unbearable. The natural reaction is to let go of your hands to relieve the pain, which forces you to fall backwards. This unnatural position places pressure on your ribcage, and your breathing is restricted. Eventually, you pass out, and your lungs may collapse if you are not pulled out…

Caution. - To release your prisoner: Two persons are necessary, one on either side. Take hold of his legs and lift him up the tree; then unlock his legs.