fremark

The act of making an underhanded comment to someone at Their expense; taking a free, cheap-shot, knowing they can't respond or reply, due to the secret or confidential nature of the content.

Shannen: Did you see the fremark that troll, Barry, left on my facebook wall?
Scott: Yeah, he knows your response will expose the secret you two share, so he's been fremarking on people's pages. You know, you can't tell him Anything he won't use to try to extort you with! lol