Knock knock jokes are considered classic question-answer puns enjoyed by people of all ages; some classic funny knock knock jokes are "Knock knock!/ Who's there?/ Aardvark!/ Aardvark who?/ Aardvark a hundred miles for one of your smiles" and "Knock knock!/ Who's there?/ Boo!/ Boo who?/ Why are you crying?" The standard knock knock joke is five lines with the punster saying, "knock knock!" and the recipient asking "who's there?" The punster replies, setting up the pun with a play on words or a name and the recipient repeats the line, asking "who?" at the end, and then the punster delivers the punchline that includes the initial response.
Another example of a knock knock joke is: "Knock knock!/ Who's there?/ Abbott!/ Abbott Who?/ Abbott time you opened the door!" "Knock knock!/ Who's there?/ Aaron!/ Aaron who?/ Aaron on the side of caution!" is an additional timeless knock knock joke.
The knock knock joke's origins stem from a 1929 children's game called "The Game of Buff." Variations became popular in parlor games and radio broadcasts of the 1930s.
Modern knock knock jokes are available from iTunes and Google Play. Free applications can be downloaded onto users' devices and can deliver knock knock jokes that are extended weekly or updated in real-time.