1. Tell him that you know he didn't really care about Sirius Black

2. Make out with Ginny Weasley right in front of him

3. Tell him he sucks at Quidditch and offer him pointers on how to stay on his broomstick

4. Loudly and in great detail, tell him how much he reminds you of Severus Snape

5. Convince him that it was Dumbledore who invented the Cruciatus Curse

6. Make him believe that he is closely related to Bellatrix Lestrange

7. Convince him that his parents used to be Death Eaters

8. Make him spend a week alone with Bellatrix Lestrange

9. Give him extra private Potions lessons with Professor Snape

10. Convince him that there's been a mistake, and that he really belongs in Slytherin

11. Tell him that if he hadn't been in Gryffindor, Dumbledore wouldn't have died

12. Make him sit through an interview by Rita Skeeter and then have to read the whole thing out loud in front of everybody

13. Make him loudly and publicly insult the Weasley Family