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1.
What some people consider the rules of hitchhiking, where the hitchhiker, upon pickup or throughout the trip, must either provide: 1)Gas for the car, 2)Some type of sexual satisfaction, or 3)Some type of drug, usually marijuana.
Hitchhiker: Yo dude, can i get a ride?
Dude: Gas, ass, or grass.
Hitchhiker: *pulls out baggie* Grass.
by punkbass_20x6 January 14, 2006
 
2.
When someone asks you to drive them somewhere, they can pay with gas, ass, or grass. Gas(money for gas), ass(a sexual favor), grass(marjuana).
Ling Ling: "I just drove you all the way to Africa. You know the rules... gas, grass, or ass."(gas, ass, or grass)
by mikec00l October 22, 2007