This is one of the best pranks I have heard about.
On November 20, 2004 at the 121st Yale-Harvard game, 20 Elis donned custom made “Harvard Pep Squad” t-shirts, applied enemy-red war paint on their faces, and set out to pull a prank on 1800 Harvard alumni. Like clockwork, these brave Elis proceeded to exude more Harvard spirit than any Cantab ever… tossing t-shirts to the lucky and unsuspecting few, and passing out 1800 sheets of red & white construction paper in perfect order to the cheering Harvard crowd. With 4:47 minutes left in the second quarter of the game, each member of the crowd raised their sheet of paper expecting to spell out “Go Harvard” as they were told by the cheering “Harvard Pep Squad.” Instead, the truth was revealed to a laughing crowd of YALE alumni and students who saw the Harvard crowd spell out in clear red letters”WE SUCK.”
(via Backwards City)