Someone i know is convinced that he has the spirit of an angel within himself, he says he is gnostic, he claims to know God and that God speaks to him and told him a secret about this angel spirit of his. how do i fight this?

i dont know if i should rebuke him, i know that the only spirit that dwells in man is the holy spirit or demons, he had this "revelation" while using acid, is he possessed and trying to maniulate people away from God? i do not believe him but i am angry that he is spouting this theory like its truth and telling everyone he knows. help!