Referring to road head, this is usually used in a sentence when someone is talking about a car ride with a girl. The rule of the road is when and if you give a girl a ride somewhere in your car and she gives you no money or gift, she must follow the rule of the road and give you road head.
guy 1: i gave cindy a ride home last night.
guy 2: did she follow the rule of the road?
guy 1: naw, she gave me $10
bill: i gave sarah a ride to wal mart earlier.
jimmy: you use the rule of the road?
bill: yeah, she tried to stop by an ATM to give me cash but i refused and made her sucky sucky