Wanna hear a ‘knock knock’ joke?

My 7-year-old loves ‘knock knock’ jokes. He can do the same joke five times in a row and each time will be equally hilarious. Watching him laugh so uncontrollably is very often funnier than the joke itself.

Knock knock!
Who’s there?
Justin.
Justin who?
Just-in time for tea.

Cue peals of laughter. Then he goes on to relentlessly repeat it several more times despite my pleas for him not to.

Knock knock!
Who’s there?
Builder.
Builder who?
Build-a wall!

“Get it? Mum, do you get it?” he would often nag.

And here’s one that has become my favourite.

Knock knock!
Who’s there?
Boo!
Boo who?
Don’t cry, it’s only a joke.

Do you have a favourite ‘knock knock’ joke? I’d love to hear it.
Please share them so I can then tell them to my son so he can change the record from time to time.