(Strip Number 5071, Original Publication Date, 3 January 1988)
Panel 1: We end the Christmas arc with Mike objecting to once again having to write thank you letters because children are evil and lack gratitude and not because John has been a big hypocrite who says it's a joe-boy job best palmed off on a flunky.
Panel 2: Elly shoots herself in the foot by telling him that writing a letter is not much to ask when a person goes to all the trouble of buying him a gift. This is because he remembers her saying the same thing about having to send Christmas cards to people she doesn't remember just because they send her one. This is a reminder that Elly's thought processes are out of whack because she should be telling him that since Marian and Jim's side of the family were absent when they sacked the Christmas tree, this is how they get included.
Panel 3: She then tells him to make it bright, informative and to tell the person how much he loved their gift.
Panel 4: When he recites "Dear Grandma, Thank You For The Underwear. Love, Michael", Elly is gobsmacked.
Summary: If it's not John telling the kids that common decency is a tedious chore best palmed off on someone else, Elly is making kids think that behaving graciously is a futile gesture imposed on them by the uncaring. This is why they don't have manners; they're raised to not have them.