Nose Avoidance Tilting is a Jeffism.
N.A.T. stands for Nose Avoidance Tilting and refers to the slight tilting of the head two people may unconsciously perform while standing opposite each other when there is an attraction between them, as if preparing for a kiss. This seems to be the only concept of Jeff's that Steve understands. Brought up by Jeff in the episode Naked, it is a sure sign that someone is interested in you, yet Jeff finds himself unable to act on the hint when he experiences it with Julia in that episode.