"Bar fly" is an idiomatic expression used to describe an individual considered to spend an inordinate amount of time at bars and taverns. The term likely derives from the small insect of the same name, also known as the vinegar fly, which is attracted to alcoholic beverages. "Juicer", "lush", and "boozer" are synonymous slang terms. The term was once a direct implication of alcoholism, though the connotation has weakened over time.
Bars and taverns were historically centers for news and business dealings, and less exclusively just places to go for alcohol. By the 19th century, many places began to specialize in just serving drinks, foregoing their previous air of formality and emphasizing cheap alcohol and a relaxed attitude. The term bar fly was likely born in the years before the enactment of Prohibition in the United States, between 1910 and 1920, as a derogatory term for alcoholics who all but lived in such establishments.
Through the beginning of the 21st century, a bar fly has become less a characterization of overt alcoholism and more an synonym with the less negative term "regular." A regular is a person who frequents the same establishments on a nightly or near-nightly basis with no specific mention of drinking to excess. Staff and management typically know a regular by name and afford him perks, such as a reserved seat at the bar. While a problem with alcohol may indeed exist, the status of an individual as a regular does not assume it.
The classic bar fly archetype is a common character in popular culture. Among the most well-known is Barney Gumble, a character on the television program The Simpsons. Gumble is portrayed as an oafish, dimwitted alcoholic who spends virtually all his waking hours sidled up to the local bar. He is hopelessly addicted to drink, and his appearance, intellect, and speech have suffered as a result. Characters exemplifying the modern connotation of a bar fly include Norm from the television series Cheers. Habitually greeted by a collective "Norm!" upon entering the Cheers bar, Norm does not display symptoms of problem drinking, but receives the warm, familiar treatment of a regular.
Given its connotations, variations on the bar fly term are commonly used by regional bands, drinking groups, and social clubs, generally in an ironic or mocking way. There are more than a half-dozen bands called The Bar Flies located in various parts of the United States, and countless bowling teams, weekend softball teams, and fantasy sports leagues. Several bars around the world are themselves named the Bar Fly or some variation thereof.