1. A person of either gender with poor judgement and no class.
2. A person with bad personal hygiene.
3. A promiscuous person.
4. Someone that enjoys anal sex.
"Person 1: Did you see how greasy her hair was?
Person 2: Yeah she's definitely a dirt rider."
"Person 1: Stacy let me do anal last night.
Person 2: I knew she was a dirt rider"
Californiadude: "yeah man earthquakes aint nothin' I am THEE Quake Rider and I will take on any faultline! When everyone else is on their ass, I'm still standing.