Social sponge
A person that tends to unknowingly adapt to be like a person or group of people that they talk to, mimicking their patterns, personality and appearence. A conformist.
Person 1: Is that Katie with the jocks? I thought she was one of the art geeks!
Person 2: Yeah, she switches to the social group of whoever she befriends, she's a total social sponge.
Person 2: Yeah, she switches to the social group of whoever she befriends, she's a total social sponge.