The Umbrella rule is an interesting one. It states “No two men shall share one umbrella. If it is raining, each should have their own umbrella.”
This is a pretty common rule, you will see it almost always in practice. However, there are some strange exceptions to this rule. One is a man who has a client for some business venture. Obviously, the proper thing to do is to cover both yourself and the client with an umbrella, or you will lose the deal.
Another exception is again a father and a son. The child is not old enough in this situation to hold an umbrella yet. I think the rule of thumb here is “only share an umbrella with someone you are willing to take a bullet for.” Obviously, that is an exaggeration, but the business man needs the client, the father is looking out for the son.
Food sharing is another example. Food (and drink) shall not be shared from one man’s plate to another. The ideal system for food distribution would be a plate with the food in the middle of the table (it both showcases the food and makes it efficient for everyone) Again, follow the rule of thumb from above to take into consideration exceptions, but I see few with this rule.
Sharing a bed. This is an interesting topic. Because there are really no defining characteristics of this rule. Basically, if there is some sort of buffer between you and the other guy in the bed, you are all set. But, you should sleep ass to ass to avoid crossing the swords, and to make sure there’s no funny business going on. Also, family trips to save on cost are permitted under this rule.
Another thing you don’t share: Women. The end.