It takes two. One to change the bulb, and the other to kick the switch.
or
Pointless
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
A Chair!
or
Because they only know their ABCs "Anybody But Clinton".
or