Did Duncan fancy Watts?

It's possible, but he already had a girlfriend. As you recall, he showed a picture that he drew of her to Keith while serving detention (although the picture didn't have her wearing any skin)

He was cruel and tried to get a reaction and start fights with everyone. Check the teacher who caught him with cigarettes (those aren't mine), a bottle of alcohol (that's just for show), and a deck of nude playing cards (those were a present from your wife). I would say he's kind of like Bender in "the breakfast club" who would rather be in detention than school or at home with his family. It's odd that the credits don't even refer to him as Duncan, just Skinhead. He is referred to by name. Why just use a generic label like Skinhead?