Paddy & Murphy are working on a building site. Paddy says to Murphy,

“I’m gonna’ get the day off. I’m gonna’ pretend I’ve gone mad”

So Paddy climbs up the rafters, hangs upside down & shouts “I’m a light bulb, I’m a light bulb!” while Murphy watches in amazement

The foreman shouts: “Paddy, go home. You’ve gone mad”

As Paddy leave, Murphy starts packing his kit up to leave also

“Where do you think you’re going?” asks the foreman.
“Well, I can’t work in the friggin’ dark!” said Murphy.