I think unusual things can be Dark as well - I mean, Gilderoy Lockhart, despite the temptation to laugh at the idiot, was a fairly Dark character, and, I think, even more Dark and dangerous because he came across as a buffoon. He was willing to Obliviate people and possibly destroy their lives (consider that he wanted to take ALL of Harry and Ron's memories - destroy their minds, basically) just for the sake of fame.
So I really like fics that seem fine on the surface, but as you delve deeper you find a baser motivation and a Darker purpose than it seems at first. Lupin would definitely be a candidate for that... :D