Bitch tax is what you pay after breaking up with someone. It refers to the value of whatever personal effects of yours they had and now will not return.
John: She has my favorite shirt, three of my CDs, and my dog, and she's refusing to give them back now that we've broken up.
Adam: That's a tough bitch tax to pay, man.
Sally: I left my shampoo, makeup, and underwear at his place. Should I call him to try to get it back?
Jane: Just pay the bitch tax and move on.
Tom: Amanda stopped by to return my apartment key, autographed baseball, and the $30 she owed me.
Kristen: Wow, you didn't have to pay any bitch tax? Nice breakup!
This is an acronym for "boys are dumb." It sounds like "bird" but is pronounced like "word." Can be modified as "BRRD" (boys are really dumb) with more Rs inserted as necessary.
Sara: So then he completely failed to pick up on my flirting, and went home alone.