I have stumbled across the following joke in Fallout 4 game:
- What is the best way to start a parade in South Boston?
- Roll a 40 down the street.
I have no idea what roll a 40 down the street means. Can anyone explain?
A "40" is a 40 ounce bottle of beer or malt liquor (usually malt liquor)
The phrase "40 ounce" typically refers to a single glass bottle of malt liquor, a form of beer noted for its high alcohol content by volume. (Source)
Large bottles of malt liquor are inexpensive and associated with heavy drinkers that don't have a lot of money. The "joke" is disparaging the people who live in South Boston as the type of people who would chase a bottle of cheap liquor rolling down the street.