Seven. One to install the new bulb and six to figure out what to do with the old one for the next 10,000 years.
or
The barman says "Sorry we don't serve food in here"
or
He was a baaaaaaaaad driver.
or
Two. One to take notes while the other screws it into the faucet.
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Two. One to hold the bulb and the other to rotate the planet.
or