If it helps any, I've seen the X used to substitute as a shorthand for the title "Christ" in a number of ways. "Xtian" for Christian, and just "X" when used in contradistinction to the letter Omega (which I don't know how to produce on this keyboard) for God the Father. Look at a Greek icon, those aren't initials, they are the first letter of words in a phrase. If you want to simplify your expression and you're with a group that knows the referent (yeah, that's what I meant to say), then it's no big deal. And if you're offended, then you just got a fantastic opportunity to exercise Xtian love, patience and forgiveness.
Merry Christmas to EVERYONE!!!