Paddy gets a job on a building site, and the boss tells him he must be there at 8am to start work, and not leave any earlier 5pm, or he will be sacked instantly. Paddy agrees, and promises to behave himself.
At midday on the Monday the boss leaves the site, and Paddy's colleagues pack up to go home, telling Paddy that the boss won't be back again that day, so he might as well go home. However, Paddy keeps his promise and stays there until 5pm, and is the only person to stay.
Exactly the same happens Tuesday and Wednesday, but when midday on Thursday arrives, Paddy caves in to peer pressure and leaves the site with the rest of them just after 12pm. However, when he gets home he hears some noises coming from upstairs, and quietly creeps up to see what's going on, whereupon he discovers the boss in bed with Mrs Paddy. Surprised and shocked, he turns around and goes back to the building site.
The following day, the boss goes off site again, and Paddy's mates tell him it's time to go home. Paddy replies, 'Not a chance! I nearly got caught yesterday!'