.
An armed society is a polite society. Manners are good when one may have to back up his acts with his life.
Robert A. Heinlein
I must admit that I'm not too fond of this one, particularly in the abbreviated form. It's too easy for others to think it refers to everyday manners, as if we would use guns to enforce "Please" and "Thank You." It's not about politeness, but civility. Not robbing and killing one another, the basics like that.