I read this book when I was 11, and I don't care who knows: I really liked it. I don't guarantee I'd like it as much if I read it again today. I'll admit I can't remember all that much about it. It's this future society run along sort of eugenic/libertarian lines. Everyone walks around carrying a deadly weapon, except for a few wusses. If somebody offends you, you challenge him to a duel on the spot. Or her, did I hear you ask? Good question. I don't think it ever came up.
The bit I remember best is near the beginning. They're having dinner at a fancy French restaurant, sitting on a balcony and eating bouillabaisse. A member of the hero's party carelessly drops a crab claw over the railing, and it lands on a table below. The guy downstairs pulls out his blaster, the hero is quicker on the draw, and honour is satisfied all round. I'm not sure if the other guy is killed or just seriously wounded - I think the latter.
At the time, I'm afraid I bought Heinlein's argument that, if everyone carried a gun and was ready to use it, people would have better manners. Look, I was 11. I still can't eat bouillabaisse without thinking of this scene.