I had been considering using one of my newer characters, one that devotes her life to the pursuit of knowledge and is basically a human Wikipedia- you can ask her something and she'll likely know, but she'll also devolve into tangents about completely unrelated things, like talking about The Lion King in the middle of a conversation. I don't really know what her compulsion would be, though, as the constantly rattling off information is more a tic than anything, and I don't really know what her act could be, either.