horizontal handshake 

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 always feel 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.

horizontal handshake by QuacksO August 2, 2019

Horizontal Clam Handshake 

Another term used for scissoring, the act where women intertwine their legs and rub their vaginas against eachothers vaginas.

Hey dude, I walked in on Susan and Betty making the horizontal clam handshake last night!

Horizontal Clam Handshake by Chris Brown (Sinny/Aerach) December 24, 2007