When your wife is a whore that can't make it through your military tour without getting dick, so she ends up obtaining a boyfriend to fill in her dickspace despite her marital vows.
My boyfriend-in-law fucks my wife while I go fight for my country.
How you are introduced to people at a party by your girlfriends sister, when the parties in question are over 21 years old and very committed to each other.
Hey Sally, this is my Boyfriend-In-Law,(name), and hopefully soon he will make my sister an honest woman.
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).