The Wolf of Wall Street has reportedly set the record for the number of times people say "fuck" in a non-documentary movie, according to Variety. Over the course of the film's three hours, Leonardo DiCaprio, Jonah Hill and their cast-mates supposedly use the expletive 506 times. That means someone utters the word roughly 2.81 times a minute. The site claims the previous record holder was Spike Lee's 1999 serial killer movie Summer of Sam, which let the F-flag fly 435 times. Wolf director Martin Scorsese has a history of peppering his pictures' dialog with profanity, and Variety claims his mobster movies Casino and GoodFellas both rank high on the fuckometer with 422 and 300 instances, respectively.
According to an anecdotal Wikipedia list of movies that most frequently use the word, Casino ranks at number five and comes GoodFellas checks in at number 12. (Incidentally, music fans may be dismayed to learn that, according to the list, the Brian De Palma–directed Scarface uses "fuck" 207 times, according to the list, not the 182 times that Blink-182 claimed as a rumored meaning behind their name, a rumor that frontman Mark Hoppus debunked in a 2011 interview with Fuse.)
Incidentally, Scorsese and screenwriter Terence Winter based the movie's screenplay on the book The Wolf of Wall Street by Jordan Belfort, who had quite an affinity for the word in real life. According to a iPad search of the eBook version of Belfort's memoir, he wrote the F-word 737 times.
The movie with the most occurrences of the expletive remains a documentary about the history of the word itself, titled, naturally, Fuck. That film came out in 2005 and features a variety of celebrities, ranging from Kevin Smith to Alanis Morrissette, dropping the F-bomb some 857 times, according to The Guardian.