The knock Knock joke is an all time classic, with millions of variables. It is also one of the first jokes kids learn to tell because of the simple premise.
Cows go who?
No, cows go moo!
Bless you and please cover your mouth next time.
Don't cry, it's just a joke.
Ice cream who?
Ice cream if you don't let me in!
Noah way to open the door?
The problem with being the "funny one" amongst your friends is that you have to be able to be at least slightly funny on demand. This is not as easy as you might think. The fastest way to get out of an awkward social moment is to drop a joke, the more awkward the moment the less funny the joke has to be.  But yuo cant go telling a dead baby joke to your boss and your friends at the pub probably wont like your office supply joke so now you have to memorize enough jokes to get you through any social setting.
Thats what I am here for. To talk you through the theory behind jokes and the basic structure of the joke so you may be able to craft your own joke to suit any situation.
This is called the "Thats what she said" Theory.