h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

You forgot to mention the ritual over who will pay for dinner in England (and probably elsewhere too). There has to be at least 3 or 4 minutes of discussion about who will buy dinner, there are no hard and fast rules for this, it can end with one party paying, splitting the bill evenly, accepting someone else's offer to pay on the condition that you'll pay next time, etc. Commenting on this ritual during the ritual is very frowned upon, and will upset all the participants. Personally, I never miss an opportunity to lean over to my neighbour and whisper in a highly audible voice, "they're playing the game".

Another related ritual in America is that of the tip. As stated in the article, one should leave enough money to cover the cost of the meal (don't forget the applicable sales tax) and some extra for the tip.

However, it is considered rude by many to comment on the amount other people leave for the tip. If one feels the tip another has left is too small, stay quiet and add a little more to your own. If one feels is it is too much, stay quiet and realize that the other person is generous. If someone else is paying for the meal, and you think they haven't left enough of a tip, leave more on the table somewhere quietly rather than berating your host for being a lousy tipper.

One of my friends used to date someone who was a waitress, and she would constantly cause a scene at any meal we ate in a restaurant, in regards to the tip. No matter how much we left, it was either too much or not enough. Eventually, due to this behavior, I refused to eat with her in public.

And rember the normal rules of mathmatics don't apply to resteruants.