A.k.a. "moocher's greeting" or "glad-handout"; it refers to where one of your "friends" beamingly approaches you with extended arm as if to greet you with a hearty palm-clasp, but instead of positioning his hand vertically the way one usually does when shaking hands, he holds his outstretched palm **upwards** so that his hand is horizontal --- this "gimme, gimme, gimme" position is how his hand is usually held whenever he is around fellow humans (duh!).
I alwaysfeel suspicious whenever someone greets me with a horizontal handshake, since it is a good indication that he is planning to ask me for a handout.
When someone shits on their hand then shakes the second partys hand with out said person knowing in an act of a agreement and promise.
similar to "Spit on it" when both partys spit on their hands and shake in a act of agreement and promise
I made a promise with Dave not to talk about the fact I cheated on my wife and after I shook his hand I found his shit on my hand.
The dude did a peasant handshake.