Find the gym in the Redsands East area. It is parallel to a bomb shop called "Weddings & Weldings". There is an alley next to the shop. Go into it and stand on the eastern wall of the bomb shop. Look in the northeastern direction to see a tall white building. If you stand in the correct location, you can see pedestrians spawning on the lower roof and falling off. You can run up to a pedestrian after they have fallen, but you cannot stand underneath the roof and wait for them to fall on you; they only spawn from a certain distance.