I have this habit when I am around certain people I act different. Here is an example. My friends can be assholes and when I am around them I become an asshole. I say shitty things an put others down. Then let's say I am around my nerdy friends and all of a sudden I am silly and nerdy and I act very intelligent. Or in a business setting i am very monotone and I am very "let's get it done". My boyfriend says I do change but I still have a hint of my actual self. 
I looked up this and google said BPD but I don't trust that but do you think this sounds like a mental illness that's anyone has heard before (I have anxiety if that helps anything)