(verb) It means to relax. You say it to people to de-stress and unwind. It can be used interchangeably with "take a chill pill" or "take a load off" Or if a conversation is too heated and it needs to be cooled down, people will say "A/C!"
steve: WOAH! STFU! YOU'RE STUPID AND ARROGANT!
ben: NO, YOU'RE SUCH A BITCH FOR EVEN CARING!
mark: you guys, A/C. A/C.
A group of 10 to 15 year old boys on Honda-Tech that aspire to own pink and orange Japanese economy cars and 48" chrome "spinna" rims. Additionally, there are also a disproportionately large group of 20-somethings that feel painting and applying decals and wings to a used Japanese car is quite possibly the best way to pick up a new "baby momma" after the old one has sold her body for crack.
Yo dawg! You see that fresh Civic in A/C? It had a mad tyte fishtankin it! R0TA 4 LYFE!