I just discovered this comedy group called Improv Everywhere. This group goes around doing large performance pranks on video and then shows it to the world via the internet. By performance pranks, I mean stunts where groups of 50 to 100 people go and either try to trick or confuse people during their day to day activities. Most recently, many people in Boston rode the subway with no pants on, prompting many weird looks from other passengers. A notable performance of theirs is their Best Buy prank that you can catch below:

If you want to check out more of their awesome stuff, make the leap to their website.