Help Me! Im Drowning!
Buy a doll and tape recorder- Ask a young girl to say into the tape recorder- "Help me! Im drowning" Over and over again. Go to the bathroom of an office building and place the doll in the toilet. Go into the next stall and wait patiently til someone comes in. Then push play on the recorder. Leave the recorder on and walk out of your stall and ask the guy - where the hell you think that sound is coming from. Once he opens the stall door and sees the doll in the toilet- Begin to freak out and ask him if he knows CPR. Run out and tell him you are going to get help.
Have some of your friends run in a minute later and ask the guy who needs CPR. When the guy tries to explain the story- have your friends beat the shit out of him for thinking a doll needs CPR. This man will never know what hit him.