Costume Debut: Halloween 2009
Honors: Hunter DA's Sexiest Costume
For Halloween in 2009, Irvin dressed up as Nymphadora Tonks. The boobs were even bigger this year, because Tonks can change her appearance at will, and was trying to impress Remus. Irvin attended a Halloween party thrown by Hunter DA, and won the award for Sexiest Costume, an honor on par with Mugglenet's Costume Contest.
Irvin proceeded to get groped by hundreds of people at the Halloween Parade in Greenwich Village (in his very first year, too!), where his breasts kept his front lower half completely dry despite torrential rain.
Don't feel bad if you're aroused by him as Tonks, you're hardly the first. He really was very sexy, and by the laws of the wizarding world, legal at the time (he was seventeen).
As a side note, this costume was the biggest group effort of the lot - Irvin borrowed items from three different people to pull it together.