James: You hexed James in the corridor for revenge as he had previously humiliated your twin brother. James sauntered up with the Marauders and surprisingly asked you to teach him and his friends the hex. You refused.

Sirius: You grew up together with both of your abusive Slytherin pureblood supremacist deatheater families being friends.

Remus: You were failing your classes but trying to fix this by studying in the library. However, you didn't understand the stuff so sat there muttering expletives until a shy but handsome Remus came up and explained the concept you were struggling with at the time.