A nasal defect in which skanky smells of shit and piss usually prevent things like flowers and baked bread from smelling properly to the smeller. Either that, or the person (his or herself) is the one who smells like shit, and thus blocks out other more pleasant smells.
Jane was diagnosed with astinkmatism last year. It's shitty for her. But, as a raunchy old man once told me, "the smeller's the feller".