Bonus trivia is closed! Congrats to Blair Waldorf (Superkink)
who were the first two to get everything correct.
Harry - Lighting Scar is from when Voldemort failed to kill him when he was a year old. First mentioned in Sorcerer's Stone. "I must not tell lies" is from detention with Umbridge where the cursed quill he was using to write lines left the imprint on his hand. Happens in OotP.
Ron - During the battle in the Ministry Ron knocked over a tank of tentacled brains who then proceeded to attack him, leaving the tentacle scars on his arms. Happened in OotP.
Hermione - Bellatrix Lestrange carved the word "Mudblood" into Hermione's arm when interrogating her after the group's capture and imprisonment in the Malfoy's manor. Happened in the first DH movie.
400 points to Ravenclaw!