Dictionary / Vocabulary / 馬鹿がうつる
ばかがうつる
to become stupid from associating with stupid people; to be infected with stupidity
Also written 馬鹿が移る、バカが移る
馬鹿が移るまえにそのような宗教に関わらんほうがいい。
You should stay away from cults like that before you turn into a moron.