Can i say this as an original Knock Knock joke? This is, I hope, an original joke. If its not, then am sure I'll find out in seconds after posting. It doesn't really work on the page, but verbally to someone else I think its ace, as it splits your friends into those who get it instantly and those who really don't.. and they often repeat the 'whose there?"" reply creating a mini repeat game.. it is funny to see how many times you can take it round before they eventually get it or give up in confu…