A face which people make, often unaware, which gives the appearance that they are smelling a noxious odor. Often times, if a person is a fartface, this is the way a person's face looks even when they are not making a face. Also, if a person is a fartface, they also have an attitude or dillusions of being better than everyone around them, which is what causes their face to constantly contort this way.
-'Have you ever met that Dan Williamson?'
-'Yes and his face smelt of farts...'
-'It's not his fault, he is a fartface, a dissorder he was born with'
-'Unforgivable'