Not Another Knock Knock Joke Please!!!

Okay, my 4 year old and 2 year old have discovered the fine art of telling knock-knock jokes, and I use the word "joke" very loosely. The 2 year-old has especially learned how to turn literally any sentence into a knock-knock joke. That's because his jokes make absolutely no sense. One of his favorites is:
"Knock-knock"
"Who's there?"
"Daddy"
"Daddy who?"
"Daddy go to work?"
He knows how to get a laugh though as he orders me to say "haha" after each joke. I think he has forgotten how to speak in a normal conversation!! Sometimes after I can't take it any longer I will tell him no more jokes. He then tells them to himself complete with the haha at the end. I figure this should be worth at least a little time off of purgatory for me, don't you think?!