I was watching an Australian comedian called Adam Hills on tv the other night. I like this joke, which he said is his favourite joke:

Adam Hills - inflatable joke

There was an inflatable boy who went to an inflatable school, where all the teachers were inflatable, all the students were inflatable, all the buildings were inflatable. He gets into trouble for bringing a pin to school, and the headmaster says, "You've let me down, you've let yourself down, you've let the school down".