Who says hello to whom?

Hello!! I’m on the road with the driving school and of course the one or other biker came to meet me and I asked myself THE question of all questions: Who is allowed to greet whom, when and how?? Does everyone greet everyone? Or does the small machine greet the one with the big machine? Or does the athlete only greet other athletes? Or does mountain riders just greet mountain riders? Would I be interested in who you greet and who you don’t… Bavaria different from Hamburg? So I don’t greet as a driving student. Hope you forgive me, but I’m really focused on not missing the next turn, Basti