A strange sort of mix (not really) of the two words 'flattered' and 'disgusted', used to show a strange feeling that no other word or phrase can quite convey. Also slight shock perhaps.
(Made up on my kitchen floor at three in the morning, sorta stoned and eating profiteroles)
Someone 1: I was making out with this guy last night, and all of a sudden I feel a hard on in his pants.
Someone 2: Oh mah God!
Someone 1: I don't know whether I should feel flattered, or disgusted - I've only known him for three hours.
Someone 2: Go for flatgusted, I think that's a pretty good compromise between the two.