Press shift 5 times to activate.
It is supposed to allow you to use either SHIFT, CTRL, ALT and the Windows logo by pressing one key, but people I know refer it to some awesome joke, as they yell "STICKYKEYS!" in random places and at random times.
Sticky Keys Guy: "WOOOOOOT STICKYKEYS!"
Random person: "Um, hi?"
Sticky Keys Guy: "YAAAAAAAAAAAY"
Random Person: "Hello?
Sticky Keys Guy: "I LOOOOOVE STIIIICKYKEEEEEYS"
Random Person: "Sigh..."