Another harmless practical joke to be played on people living in multiple story apartment buildings is as follows: Knock on victim’s door. Say, "I’ve got to use your window, someone’s about to jump from an apartment above yours." Run to window and look outside, but don’t let victim look.
At this point your accomplice dumps a rag-filled dummy either from the window above or from the roof. The dummy should be fully closed; for added realism put some plastic bags of fake blood inside the clothes. On the sidewalk below, a third accomplice puts down a plastic sheet, then covers it with a sheet painted to resemble the sidewalk. After the body hits, let the victim see the gore, then convince him to run down and help while you stay and call the ambulance.
As soon as the victim has left, signal your accomplice to remove the sheets and the dummy and head for some prearranged hiding place. Then you leave the apartment and disappear somewhere in the building; later, you make your way downstairs and leave. The victim will race downstairs expecting to find a dead bloody body and will instead see only clean, empty pavement.
Of course, it is best done late at night since the joke would be spoiled by a passer-by who informed the victim of the "body’s" fate. The fun comes imagining the victim trying to convince the police or anyone else of what happened!