I don't understand why, instead of meeting with them to be admonished over something as stupid and innocuous as an FB post, you didn't meet with them just long enough to hand over a letter from your attorney. Oh yeah, and while handing it to them, you should have had the biggest "you can start shi**in now" grin anyone has ever seen. And then gleefully walked away gotten in your car and driven off, all the while smiling at them with that same grin.
But then again, that's me.