The rule
If two of you are under one umbrella, tilt it towards the other person and take the wet shoulder yourself. If you have an umbrella and someone beside you hasn't, offer it, and see them to wherever they're going, or at least as far as the door.
Why it matters
It costs you a damp jacket and nothing else. The other person doesn't have to thank you or even mention it, and that is rather the appeal. Most courtesy is a matter of noticing who is getting the worse end of a small thing, and quietly swapping places with them.
How to do it well
- Hold it high enough to clear the taller of you, and tilt it their way without making a performance of it.
- Walk on the side nearest the traffic, because a passing car can soak someone faster than the rain.
- At the door, let them go in first. Shake the umbrella out yourself, away from everybody else.