Yeah, everyone knows the meaning of “bar-fly.” Still, it’s nice to get the full definition. Let us turn once again to the dusty Dictionary of American Slang:
bar-fly n. 1 A person of either sex who often and protractedly drinks at a bar; a heavy drinker of whisky; a souse, a tippler. 1928: “Andy Jackson, Kit Carson and General Grant — all good American bar-flies in their day.” B. de Casseres in Amer. Mercury, Aug., 133/4. -> 2 Specif., an alcoholic who frequents bars in order to beg or mooch free drinks from others.
Dammit, I do not mooch drinks. How dare you, Dictionary of American Slang. How dare you.
(Pic from Wikipedia. The other photos on that page are pretty disgusting.)