Slang referring to someone, or a group of people who are dirty, ghetto, and smokes cigarettes and/or do dirty drugs like speed.
Comes from the combination of the words "ratchet", "pack", "dart" (being slang for cigarettes) and "gang".
Does not refer to just anyone that smokes cigarettes.
Every highschool has a ratchpack dartgang. Simply look to the smoker's corner for the dirtier looking kids who are always trying to bum smokes off of each other.
Jim: What's with those kids smoking outside the school all the time? They always try to bum smokes off me.
Andrew: That's just the ratchpack dartgang.