Think nothing of it.
If he does it again- state- in your best mafia voice.
"Ahhh... You greet everyone with your right hand, but me, your left. Coincidence? or, how
sinister of you." (smiling)
"You know what sinister means don't you? Knives even still legal up here? Just so you know, I don't like a knife fights, so I
shoot from the right"
Give him a big chummy hug (Stick right finger into his waist and smile as your left hands are locked as you pull him in tightly. ) "So good to see you bro!"
...click....
Laugh loudly- mafia like
There's nothing wrong with psychopath.
edit- I am left handed and I approve this message.