Occasionally, one of my co-workers will extend his arm like in a handshake, but with a closed fist.   I refuse, then explain this is a symbol of aggression and rebellion.

  It was an expression of the Black Panther organization years ago.  Now revived by the wife of the Resident.  Showing clearly a spiritual heritage to those black radicals.

The open hand is the true symbol of friendship.  Showing no hidden agenda.