Possible Clues:

• Insider's knowledge
• Part of a fraternity ritual, perhaps
• Greeting that might include a couple of high fives
• Complex series of daps, chest bumps, etc
• Greeting between members of an exclusive club, and what's hiding in the answer to the starred clues?
• Greeting known only to group members
• . . . for members only
• Private club ritual, and a hint to this puzzle's circles
• Order confirmation?
• Members-only signal