There's a big difference between singing karaoke for a few friends and singing karaoke for a few thousand strangers.

Heineken recently pulled off a very cool stunt in which it got people to step into a bar to belt out a few Christmas songs. What they didn't realize was that there were cameras ready to show the performance at an NBA arena, in Times Square or in cabs across New York.

Watch what happens when these singers find out what's going on. What would you do -- sing or walk away?