A pretentious way of saying the word "dirty", If a British accent is applied, the definition seeminly becomes more pointed. Duhty has the same meaning as dirty...just with more disgust. Can be used to describe anyone or anything that's nasty, unkempt, vile, hygenically unsound, or vulgar. Also a slang term for very drunk.
Laurie and Walter took one look at Belinda carrying on with that snaggle toothed Armenian circus performer and knew immediately that she was a filthy, duhty whore.