Um... guys that cosplay (well). :D
This section is kind of a moot point for me since I'm in a relationship, but whatever.

People who hurt others. Seriously... Very little pisses me off as much as when someone makes a rude comment about someone else and the person's feelings get hurt.
Don't like someone's cosplay? That's nice. Keep your opinions to yourself, or voice them quietly to a friend.
Don't like someone's AMV? Ok... give them advice to help them get better.

This is my biggest pet peeve.

I got into anime in high school (sometime around 1998, I think) and started cosplaying/making AMVs/attending cons in 2003. I've cosplayed as Yukino Miyazawa, Vash the Stampede, Riku (Organization XIII), White Mage from FFXI, and Van from Escaflowne...
But my love is Fullmetal Alchemist. Ever since I began watching this show I haven't really wanted to cosplay much else. I love the pain and sacrifice and love that are shown throughout, and cosplaying as Edward is the most fun I have at any convention.

Claims to fame (all from AnimeBoston):

2005: Atonement AMV: Best in Show/Best Drama. Masquerade Honorable Mention, Accessory.
2006: Conter les Heures AMV: Best Romance. Edward Elric in the cosplay chess.
2007: Roydor the Burninator AMV: Judge's Choice. Edward Elric in the 18+ Dating Game. Masquerade Winner, Best Accessory. Masquerade Winner, Best Performance (novice).

Take the Magic: The Gathering 'What Color Are You?' Quiz.