The strongest response to a sneaky blow is silence.

Especially when you are expected to respond. The longer you pause, the better. Let them think what's on your mind. Let them consider options for your answers to their meanness, startle at every stranger who comes in, see you in every random aggressive fake and in every sharp quote that you repost on your wall. A person who has treated you meanly will definitely think that these are all your machinations. It would never occur to him that intelligent people do not exchange for any nonsense, and if they serve revenge, then as a cold dish. And the smart ones do not take revenge at all, they just live their lives. They are just happy!