The act of pretending to "set up" for a high five, only to scream "Betrayal Five" and then to slap the chest area of a friend. This is normally done to throw the friend off-balance or to steal something that they have. This term was coined by Todd in the TV show Scrubs.
Steve: Dude, I just found a $20 bill laying on the ground!
John: Sweet! ...Betrayal five!
*John slaps Steve, Steve drops the $20 bill, John picks it up and walks away.*