Sirius Black high-fiving Lily Evans every time she raises her hand in class.
Sirius asking James to high five her when he is too sick to come to class.
Remus Lupin doing it with a sigh and an immediate apology when neither Sirius or James is available.
Peter being overly enthusiastic about being asked to do it, and slapping Lily in the face by accident.
Let me just say that sirius endured 12 years of Azkaban and 2 years on the run but his home-grimmauld place-that’s what was intolerable for him, and if that doesn’t tell you everything you need to know about his childhood idk what does.