Quote Originally Posted by NzProjeKt
I dont know about the "Southern Definition" of it... There really isnt a secret meaning behind it.

Lots of rappers use the term.. It represents riding illegit or riding around with drugs, guns, or other illegal shit.

Ex. My homeboi's tag is expired.. So everybody tells him that he is riding dirty.
Yep, I figured the song explained pretty well what ridin' dirty meant. Guess not LIRL!!