Micro-toxic

micro-toxic (adj.): Describing individuals who fake non-toxicity while frequently resorting to passive-aggressive behavior and exhibiting traits of jealousy.

Jack, a self-proclaimed supporter of his friends' successes, often masked his micro-toxic tendencies. Despite his seemingly kind demeanor, he would subtly undermine their achievements through backhanded compliments and snide remarks, revealing his underlying envy and passive aggression.