So here's a thing -- don't have a Facebook policy at your shop. Just don't have one.
Thing is, calling someone a douche canoe is just something they could normally be fired for. BUT. And this is a giant "but". If someone writes on Facebook "My boss is a big jerk and we don't get paid well enough" and especially if someone else from your company chimes in with "Yeah" you can't fire them for that.
Clearly I have too much time on my hands dealing with renders today.