The most common one in our house is "Fair does not mean equal." And sometimes, when they've really ticked me off with the "that's not fair!" cry, I will make them recite the definitions for fair and equal, to re-emphasize it. They know perfectly well what they are, but when they have to actually define them, it usually helps it sink in better.
My children have never in their life told me I'm mean. Nor have they ever said they hate me. (We don't allow that word to be spoken in our house)
It may well be that I will hear both before they reach 18, but I certainly hope not. I treat and speak to my children with respect (so that they learn how to do the same). I give them reasons for what I say. If they start to argue it, I simply say, "This is not a debate. I've told you what needs to be done, and I've told you why. Now I expect it to happen." And they know to stop at that point, or they will end up losing a privilege.
I, also, have used the one Angi C. has........ just the other day, as a matter of fact....... my children wanted to do something and I said it wouldn't be worth it for the short amount of time we had. And my son said, "Well, we think it would be worth it, and it's two against one. I thought you said this is a democracy!" (Oh, how I laughed inside!) Then said, "Our country is, sweetie. Not our family. Our family is a benevolent dictatorship. And you know which of us is the dictator!" And smart kids that they are, they didn't even suggest Dad. They know who's in charge. ; )