Q: How many gypsies does it take to change a lightbulb ?
A: None, but you lose a lot of light bulbs.
Note: None because gypsies don't have mains electricity, and the losing is a play on the larcenous reputation of Gypsies. You give a Gypsy a light bulb and ask him to change the hallway lamp, pretty soon you have one less light bulb and the hallway lamp is still out.)
Q: How many Helmsley employees does it take to change a lightbulb ?
A: 100: 99 to try, and one to fire them all.
Note: Leona Helmsley is the owner of a New York hotel who was a terrible person to work for. She fired employees at little or no provocation. She was so nasty to her employees that she was known as the "Queen of Mean".)
Q: How many pot growers does it take to screw in a light bulb?
A: None, they use fluorescent bulbs instead.
Note: Fluorescent light is closer to natural sunlight than an incandescent bulb, so anyone using artificial light (which pot growers might do to keep their crops covered and safe from flying, prying eyes) to grow stuff would probably use fluorescent light rather than incandescent.