1. With a backpack on and another in a corner of a room, approach corner and go prone, facing in so your legs clip through the wall
2. switch your backback with the backpack on the floor
3. you should have broken legs and ruined pants. Well done.

This first happened to me in the two-story silver industrial building north of Balota airstrip, in the little upstairs room. I had an orange mountainpack on and switched to an improvised backpack on the ground.