Legal Question in Civil Litigation in Florida

If it's derogatory and untrue, puts you in a false light, or falsely claims that you committed a crime, disparages your business practices, have a sexually transmitted disease, or (if you are a woman) are "unchaste". (really) You may have a claim.

If it's just nasty comments, true, or obviously silly impossible stuff, like:

"George is a jerk, has 2 left feet, and is from Mars" then it is not actionable.

Your question points out the hazards of participating in an "open forum" like facebook.