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A slang term used to describe someone or more than one person (can be as large as a business or any other entity) who is extremely unreliable, unless they want something from you. To put these dirtbags in their place, one must confront them directly face to face. This term is different than a flake, as a fly by night DOES contact a person, but only when they want something, whereas a flake or flaky person DOES NOT.
Tim was such a fly by night about turning in that homework for our group, he got us an F! But then when he wanted a ride home from the bar, he contacted us left and right! That guy can walk his ass 3 miles to get home!

Kurt's fly by night attitude caused him to not be liked by his friends, and for him to only get sex from more undesirable types of women with hairy vaginas.
by johnnyb69 January 31, 2010
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2
an unprincipled person who just gets involved with someone or a job to meet their need and evacuates to next donor.
Watch out Kim, he's a fly-by-night, he'll use you and be gone in the morning.
by prodigal's boss December 23, 2014
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Song written by Rush in their 1975 album Fly By Night. Contrary to their debut album, Fly By Night was the first to express elements of Progressive Rock the band is known for
Person 1: Did you hear Fly By Night in R40?
Person 2: No, it wasn't in R40
by newhavenrailroad January 30, 2017
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After I pull this last Bank job I'm gona fly by night... You know isa got the ghz. Isa hertz'n so bad I'm gona fly this old koop by night back to alie-bama get's some good grits.
by itichie_nocanpo October 17, 2006
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Type of contractor that takes %50 deposit from home owners in new communities then disappears over night with multiple hundreds of the unsuspecting victims loot.

To get high in the evening.

To start a bender this Friday that steamrolls Monday meetings.

A magic carpet ride when you rent a limo bus for an out of town party tour for the summer and go on tour singing live operatuneist.
Some of them irrigation contractors are fly by night so be sure to ask for their certification # from Centre For Irrigation Technology.
by Theoraan The Verst October 23, 2016
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