Combines the words "Fly" (Kool in a ghetto like manor) and "Fish" (an aquatic creature with gills)
word can used to describe someone that you think just said something cool and/or funny.
Make sure that the person you call a fly fish knows the definition or else you will sound like a douche bag.
Austin: "hahahahahaha-you said 'duty'!"
Gabe: "OH, YOU FLY FISH!"
Outsider: "You guys are queer"