This vague rap slang is not very popular and common in the urban community so we had to research hard just to figure out its meanings. As a result, we discovered that 40 bars actually have two meanings.
The first one refers to a place, club, or bar where older men can go to find women that are typically 40 years younger and “create relations.” An example of its use is:
“Michael Douglas was rumored to be a patron of 40 bars.”
The second meaning of 40 bars calls back to Allen Iverson’s forgotten rap single. It is generally used to describe some absurd, weird, or forgettable song made by a famous person.
“While Damian Lilliard is a god in basketball, his rhymes are 40 bars.”