I have no clue what it could mean. I was drawn to watching it though when he was doing it. You get a hand on your shoulder, you get a pat on the arm, you just get a quick hand shake. Could just be "part of the deal" move, like being dominate with the handshake towards other men or could be signaling to someone else to take note, this person gets the cold shoulder while that person does not. Or, this person in involved, and this one, and this one but, this one we dont care about. lol.