nobody except those called Lennard will laugh at this Joke. Usually when a Lennard joke is told all the people in this world and other worlds called Lennard will start laughing. So if you have been wondering why Lennard has been laughing so much its because of those Lennard Jokes.
Note: Very popular expression in Germany where this is called a Lennard Witz
Fred: Why is Lennard laughing?
George: Someone somewhere must have made one of those crappy Lennard Jokes.