Never stops me from treating them exactly as I would if I didn't know who they were played by. Ask Kanye or Quas. We fucking fight each other WAAAAAAAAY more than we would ever roll together.
A few times I was tempted to set something up, but the one time I had a "perma" those assholes ranked to hero without me and then deleted while I was left with no support alone in the Cabal :) That was many years ago, and at least one of those people doesn't play (I don't talk to the other person anymore for various reasons).
Exceptions to this: I tend to loot people I know aren't that great at PK less than I would people who are good at PK. Yeah, that's probably bad RP but there it is.
Another interesting tidbit is sometimes I interact with characters more if I know who plays them. I knew Alex was Eleagra right away and while I played Ghrim I was really upset that he character assassinated me constantly, that never changed how I went about dealing with Eleagra in game. In fact, I was one of her biggest fans. And I'm glad I got to challenge myself against someone that is obviously extremely skilled at PK.