Knock Knock
Who's There?
Doctor
Doctor Who?
Doctor Green, it's Tuesday, I always come at this time, to read your vital signs and check your cancer isn't too bad.
Yes, of course, please come in.
This joke is based on the following traditional knock knock joke, but I have put my own comedic twist/slant to it:
Knock Knock
Who's There?
Doctor
Doctor Who?
(The joke being that the man at the door is suggesting that maybe it is a Time Lord knocking at his door....ha ha ha...I think my version is far more plausible.)