Charles B. Pierce wrote the line "Go ahead, make my day." The line was inspired by a warning that his father would say to Pierce when he was a child. According to Pierce, his father warned him "When I come home tonight and the yard has not been mowed, you're gonna make my day."
The highest-grossing of the Dirty Harry film franchise.
Of the five "Dirty Harry" movies, it was this movie that used the catchphrase "Go ahead, make my day", whereupon it became synonymous with the Harry Callahan character and became popularized into the vernacular of popular culture. Although Clint Eastwood made the phrase "Go ahead, make my day" famous, it was originally used a year earlier by Gary Swanson in Police Station - Turno di notte (1982). Swanson, who played a Hollywood vice cop, said the line, "Go ahead, scumbag, make my day", to Wings Hauser, who played a pimp, during a bust. The quote is often erroneously attributed by most people to be from the first movie of this franchise, Ispettore Callaghan: il caso 'Scorpio' è tuo!! (1971). The phrase was also voted in a 2005 poll by the American Film Institute as the number six most memorable line in movie history. The phrase was so well publicized and became so popular that many members of the public knew about it by the time the movie opened.
The screenplay was originally written for a non-Dirty Harry movie with Sondra Locke, who was aging out of leading lady status at the time and trying unsuccessfully to develop starring vehicles. When she couldn't get any studio to finance it, the revised script, by Earl E. Smith and Charles B. Pierce, was re-written by Joseph Stinson into this "Dirty Harry" movie.