1. Because they met on a train, much like JKR and her guy.
2. Because she's just as sane as he is.
3. Because they look cool together.
4. Because he told Hermione not to insult "one of the only people that believes him".
5. Because she went with him on the Final Battle.
6. Because she comforted him after Sirius' death.
7. Because they understand each other.
8. Because he likes her knack of pointing out uncomfortable truth
9. Because he thinks she's cool
10. Because he asked her out.
11. Because Potty lurves Loony.
12. Because she wanted to dye her eyebrow too.
13. Because he liked her appearance at the party.
14. Because they were under the mistletoe.
15. Because she helped recruiting the DA.
16. Because they looked at the Ravenclaw Diadem together.
17. Because he didn't want her to get hurt.
18. Because they hold hands in the movies.
19. Because normal is boring.
20. Although we're not the majority, our ship will never sink