In English-speaking culture, a milkman joke is a joke cycle exploiting fear of adultery and mistaken paternity, insinuating that a woman had cheated on her husband with the milkman.^[1]

This class of jokes has its roots in the early part of the 20th century, prior to the regular availability of milk in supermarkets. At that time, milk in glass bottles was delivered directly to customers' houses by milkmen, generally in the morning. Typically, men were the main financial supporters of their families, while women tended to remain at home to care for their children and house. As the milkman would visit the home at a time when the husband would be away at work, this created an opportune situation for adultery.

Often times, a different profession will replace the milkman in various jokes. For instance, in Spain, 'milkman' jokes are told about butaneros: persons who deliver butane, bottled fuel gas, to households without a pipeline gas hookup. Similar jokes referring to other professions, such as postmen, plumbers, pizza delivery drivers, and swimming pool cleaners, are also known.