Knock, Knock......
.....whos there?.....
is there anybody there?.............is this a seance?
Mary
.....Mary who?...
Mary Christmas!!!!!!!
I don't get it
Ok try this one on someone.
Me: Do you want to hear the best knock knock joke ever?
Friend: Yes
Me: Ok you start
Friend: Ok Knock Knock
Me: Who's There?
You'll be surprised at how long they'll wait to see what happens next.