Lemonade.
or
Five: One to change the bulb and four to pull the ladder out from under him/her.
or
Three:
One to write the light bulb removal program,
one to write the light bulb insertion program, and
one to act as a light bulb administrator to make sure nobody else tries to change the light bulb at the same time.
or
He was a baaaaaaaaad driver.
or
Sure, Dick and Bob had a bunny!
or