Mother asks little Johnny, as they wait for the bus, to tell the driver he is 4 years old when asked because he will ride for free. As they get into the bus the driver asks Johnny how old he was.
“I am 4 years old, “says little Johnny.
“And when will you be six years old?” asks the driver.
“When I get off the bus” answers Johnny.
This joke is included in the Black Book of Jokes. You can order it from here.