The joke was that bad it merited an apology. Not just that it was a knock knock joke. Now that I’ve explained it that probably makes my small attempt at humour 100 times funnier.
At the end of time, the four horseman of the apocalypse were sitting on their horses, admiring the destruction and pain they had laid upon the earth, when they started telling each other knock knock jokes.... Knock Knock Who's there? War War Who? Warm Pouch was a bigger **** than any of us!