"Hey dude I got drunk and watched a gay porn with some poo daggers in it"
" One why did you watch a gay porn and what is a poo dagger"
"Man i was drunk but its a gay guy because when he fucks a guy in the ass he gets poo on his dick or "dagger"
"I think you might be a poo dagger"
The use of any gay related word in a negative connotation. It is often used as a response to idiotic statements, observations, ideas, jokes, etc. Fag dagger is often used in its shortened form "fag dag."
Dude 1: "Brad Pitt looks handsome in this picture."
Dude 2: "Dude, you are such a queer."
Dude 3: "Nice, fag dagger!"
or
Dude 1: "Shut the fuck up you homo!"
Dude 2: "Why you gotta throw a fag dag, man? My mom can hear you."