Mopery refers to the act of a minor offense or the breaking of an imaginary law in some contexts, while in others it is used to refer to lollygagging and loitering.
“Mopery” originates from the Shakespearian word to mope which was used to refer to feelings of apathy as well as acting unconsciously and without any composition whatsoever.
The titular phrase started appearing in its current form in judicial contexts in the early 1900’s, and it started gaining ground following the 1960’s, when a crackdown was commenced against Hippies and Wooks, who were seen as a menace to society.
In the second half of the 20th century, “Mopery” saw a significant rise in its popularity, with several authors like Thomas Pynchon, Dashiell Hammett and Joseph Heller adopting the term in their books.
It was also featured in the 1984 comedy flick, Revenge of the Nerds, where it was defined as “exposing oneself to a blind person”, establishing the newer sense of the word, according to which, the subject has offended a nonexistent or arbitrary law.
“Mopery” was first defined on Urban Dictionary in the aforementioned sense on January 18th, 2003, with several other entries following in the subsequent years.