Is there an English saying: for people that you cope with, having an infectious impact on behavior? I didn't had any characters left for the title question, so please read the intended question in its entirety: Is there an English saying for people that they cope or spending time with (implying friends and acquaintances), that have an infectious impact on one's behavior as well. As someone would immerse himself/herself in their culture and adopt the habits from them. Something that says that behavior is reciprocal by the time spend with friends or associates. I hope this is clear.