Knock, knock jokes would be so polite, if they weren't so rudely bad, with one notable exception.
Ask at your dinner table: Have you ever been startled by someone walking into the room unannounced? Have you ever startled someone else by walking into a room unannounced? Does it matter if the person coming in lives there and has every right to be there? What if the person in the room is expecting the other person to arrive at any moment?
Q: From where do we learn that this is a problem and that one should first go "Knock, knock"?
A: From the High Priest's robe. Try to picture this:
On the robe's hem they made pomegranates of turquoise, purple and scarlet wool, twisted. They made bells of pure gold, and they placed the bells amid the pomegranates on the hem of the Robe, all around, amid the pomegranates. A bell and a pomegranate, a bell and a pomegranate on the hem of the Robe all around.... (Ex Ch. 39)
The rabbis of old asked, What are the bells for? The answer - so that the Priest - the Cohen - would be heard before he entered the Holy of Holies. But that's strange - who's there to hear him? The answer is, no one but God, and God presumably knew he was coming, right?
From we derive that it is good manners to knock before entering a room, even if it's your own room and people are expecting you, it's not nice to startle them.
So here's the world's only polite knock-knock joke:
With apologies (;-)>
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