I would be very unhappy if a coworker added me on FB immediately after joining, and I'm the kind of person who's okay with having some coworkers as FB friends.

I would be very unhappy if a coworker added me on FB immediately after joining, and I'm the kind of person who's okay with having some coworkers as FB friends. I probably don't know them, and now I'm in a position where I need to reject an offer of friendship from them.