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1.
The things you do out of obligation to friends in your life with no tangible expectation of payback.
Person 1: "Man, why do I have to invite Sheila's loser boyfriend? It's my damn party."

Person 2: "Suck it. Friend tax."
by any name will do February 11, 2007
 
2.
Taxing your friends or partners by taking a portion of they're meal.
Friend 1:"Hey you just jacked my fries!!!"

Friend 2:"I didn't jack them! That was Friend Tax."
by L33TNINJ4Gurl October 19, 2009