I don't think it's too much of a secret.
There's the Young Onez group with DeRozan, Weems, A. Johnson and Ed Davis. They probably hang around with Joey Dorsey, Julian Wright, Bayless and Jerryd Bayless because they seem to have fun around each other.
The Euros are less outgoing, whether it's culture differences/language barriers or whatever other reasons.
Then there are the people like Reggie Evans who is respected by everyone.