A dance that can only be performed perfectly by one individual. It's often done as a source of entertainment in front of large groups of people who will proceed to mob around the awesomeness and chant the beat that is necessary for the dance to be performed. This chant goes "greg. greg pepe. greg gr greg gr greg pepe." And when spoken aloud the individual will magically appear flailing about in dance.
An alternative definition is; a potential fire hazard in high school halls.
Did I miss anything at 100 nights dinner?
Yeah, you missed the greg pepe dance, it was awesome.
Why's that guy's face all scarred up?
He was in a school building when the fire alarm went off, but he didn't get out fast enough because he was mesmerized by the greg pepe dance in his way.