while shaking someone's hand, proceeding to stick your thumb in your butt and yell out in a German accent "Thummin Mine Asshole"
Friend 1: I met my girlfriend's parents yesterday
friend 2: how did that go?
friend 1: good. we did a vietnamese handshake.
friend 2: what's that?
Friend 1: we all stuck our thumbs in our asses when we shook hands and yelled out "thummin mine asshole" in a German accent.
There is nothing quite like sticking your thumb in your ass while shaking somebody's hand.