Originally valley girlgang, the phrase describes a friend group who not only do the exact same things but whose entire personality revolves around being each other's friend and mimicking their personalities. The don't necessarily look the same; however sometimes they are exact clones
Dave: Hey look it’s that girl you used to like
Jake: Yeah but not since she joined a valleygang
A group of teenage boys who smoke weed and get in trouble at school constantly. They are hated by all the teachers and very good students, but are loved by everyone else because they are too funny to hate.
Person one: What just happened?
Person two: FUCK DAIRY QUEEN, BASKIN ROBINS GANG NIGGA
A group that is filled with people who are complete dirt balls basically meaning they will do anything with no fucks given for anyone. This group is usually associated with dirt Ball sports such as Wrestling.
"Yo did you hear about that hoe hooking up with Jake!" "What no way he must be a part of Dirt Ball Gang! What a filth!"