Always the contrary one, he has decided to be James Potter, Harry's father. Note that apparently James has the same sort of round glasses that Harry does and also wears a robe with a Gryffindor crest, so I pointed out that everyone would think he was dressed as Harry. To which he responded by grabbing one of those "My Name Is" nametag stickers from work and writing "James Potter" on it. Ok, that works.
I don't often do costumes either, but when I do, I go all out. My caching partner is very familiar with the Potter series, so I asked him for costume suggestions. It should concern me deeply that the first thought that came to his mind for me was an evil witch, but upon reflection I decided to go with his suggestion because it looks like a seriously fun costume. Apparently this woman is named Bellatrix Lestrange...I need to look her up before the party though since I know virtually nothing about her.
There is a commercial costume available, but it looks cheap and crappy. There are also very authentic-looking replicas available online, but they cost a bloody fortune. My solution was to put together my own version. A quick trip to a thrift store yielded two black dresses that I can cobble together to yield the long ratty bottom and the laced-up top (thank you Mom for all the sewing lessons!), and Amazon took care of the rest of it: a bird skull pendant, belt/corset thing and fishnet stockings. The whole thing together might have cost me 35 bucks and it will be entertaining as hell to show up in this outfit!!