1640s, "causing bias or prejudice, predisposing the mind to favor," present-participle adjective from prepossess. Opposite meaning "causing agreeable first impression" is attested by 1805.
"causing disgust, offensive to the taste physically, morally, or aesthetically," 1754, present-participle adjective from disgust (v.). Related: Disgustingly. Disgustful "causing disgust" (1610s) was "Very common in 17-18th c." [OED].