Statue of Happiness
Head to the Statue of Happiness on Happiness Island via helicopter. Have the helicopter drop you off on the very top of the statue. You'll find a sign up there that states "No Hidden Content Beyond This Point", but it's a lie. If you head inside of the statue from this area, you'll find an actual beating heart inside the statue.
Fire Truck Madness
If you boost a fire truck, press the fire button while driving around. This will allow you to shoot the super-powerful water cannon at anyone around you. Watching people react to getting shot with high-speed water is hilarious.
Prank Calls
Here's something funny to try. During your adventure through Liberty City, you may find phone numbers written in inconspicuous places, such as on the side of a building or in the subway. If you dial these numbers, you'll usually get someone on the other end who you can subsequently prank.
