I honestly think there is a difference from fun and selfishness. Fun has an obvious meaning “Provides amusement and/or enjoyment for all included.” This does not mean knocking on elderly civilian doors and wasting their time/amount to live. This means when an elderly person risks his life walking down steep stairs or dangerous furniture placements thinking there is actually an important message/package and just opening the door seeing nothing, much disappointment and stress. This is also illegal from the Humans Right Clinic 2012 law. This is also much discrimination to people.
A Christian view of the situation is to always respect the elderly as it can hurt, this can be physically or mentally, but it still hurt elderly people physically by trying to get to the door. There are many commandments which can fight for this point.
A Muslims view of the situation is to always respect the elderly and your young, this also can be illegal to Muslims. The Profits for their advice is to respect all people such as elderly which means knocking on peoples doors is not respecting elderly / young.
I hope this helped.
Great advice showing an understanding of a range of religions and beliefs.