(Verb) Comes from Western Colorado slang insults. It refers to a man who drinks cum out of another's ass with a straw.
(Adjective) An insult for someone who shocks you with their stupidity or aura of annoyance.
Guy 1: "Dude, I think Gnar Kill is like the greatest band ever."
Guy 2: "You are such a feltcher man."
(Verb) When two guys dig up a dead woman and soak her in a bathtub for a while, then one eats her out while the other one pushes on her stomach.
"Oh god.. That kid is here? He's such a munger."