What is the best or funniest "KNOCK KNOCK" joke you have ever heard??!

Question: What is the best or funniest "KNOCK KNOCK" joke you have ever heard!?!?
Answers:

knock knock,
Who's there!?
Doctor,
Doctor Who!?
You just said it!!!

Ha ha cracks me up everytime :-)Www@Enter-QA@Com

The answer content post by the user, if contains the copyright content please contact us, we will immediately remove it.