In the 20 years since the film was released in July 1998, the conversation about political correctness in comedy has evolved and progressed, and like Mel Brooks with his beloved-but-more-blistering-than-ever Blazing Saddles, the Farrellys find themselves the auteurs of a body of work that most likely would not get made in the same way today. Also like Brooks, though, the films they made are not only defensible, but vital. They are brave comedies, films that dare you to laugh past your preconceptions about what you can or can’t laugh at, and they were made by smart people with more on their minds than simple jokes.

There is a through line to the work by Peter and Bobby Farrelly, but it’s so subtle in the way it works that it’s easy for casual viewers to not only miss it, but to even misinterpret it. It’s easy to say that a film has heart, but the only way you can really judge the content of that heart is by paying attention to the real targets of the comedy. The Farrellys may deal in broad, outrageous, often scatological humor, but they use the most lacerating part of their wit to puncture truly deserving subjects.

Even the title of their film hides a sinister edge. There’s Something About Mary could be the title of any buoyant romantic-comedy trifle, but in the context of this film, it can also serve as a vague explanation of what it is that transforms each and every guy who comes within spitting distance of Mary, played by Cameron Diaz, into a sociopathic creep willing to cross any line to possess someone in the unhealthiest of ways. Because that’s really what this film is about. Mary is this beacon of decency, adorable and funny and vibrant, and her life is a parade of morally vacant scumbags who will lie and cheat and do anything to simply have her. There’s no indication that any of the guys in this movie would be capable of an ongoing relationship of any kind. They’re just creeps, and there’s just something about Mary, and that’s plenty of fodder for the Farrellys to then paint this big, sprawling portrait of curdled masculinity.

How do you take something that dark and transform it into a film that played like a weapon in theaters? For viewers who weren’t there, it may be hard to imagine the reaction to the film’s biggest set pieces. One of the reasons people went back to see Mary repeatedly in theaters or on home video was simply to hear the jokes they missed because the audience was so busy melting down from laughter. It’s been said that horror and comedy are closely related genres because they both depend on evoking an involuntary reaction from the audience, and the Farrellys knew there was only one way to fine-tune that involuntary reaction: test screenings. Some filmmakers fear the process, but the Farrellys are strong believers that the best joke is the best joke, no matter where it comes from.

While they are the final arbiters of funny in their films, the siblings are impressively collaborative. The Mary screenplay is credited to Ed Decter and John J. Strauss, as well as the Farrellys, and they have always used roundtable punch-ups to get a script ready for a shoot. In essence, they test the thing on both ends, first by running the script past their funniest friends, daring them to make jokes and scenes better, and then again once they’ve shot the film, trying different combinations of moments with audiences until they find exactly the right cut.

While both Kingpin and Dumb and Dumber were strong comedies, packed with big laughs, There’s Something About Mary feels like the master class they were building to the entire time. The opening sequence, featuring young Ted (Ben Stiller) and young Mary (Cameron Diaz), starts on a high note most films never reach, with an uproarious and startlingly graphic zipper accident. The moment you know you are in the hands of comedy madmen is when they opt for a quick, nearly subliminal close-up of the “frank and beans” that are all stuck in the zipper. It is exaggerated and ridiculous and horrible beyond measure, and it’s exactly the touch that you would never get from other filmmakers. The Farrellys continuously test the audience to find the line where viewers stop laughing at horrible things, and the directors cheerfully demolish almost any target in the process.

But when you look closer, when you really consider the way they cast their films in both starring and supporting roles, the truth about them is apparent. The Farrellys are relentless champions of the unseen, the underdogs, the less-thans. They have been remarkably progressive about hiring people with disabilities and then casting them in roles where the disability has nothing to do with the film. It is important to the Farrellys that the worlds in which their comedies take place actually look like the world around us, and they understand how potent that erasure can be, where even the extras in the background are all homogenized and perfect. They understand that there is no merit in heaping more scorn on people who have already been marginalized. Instead, the Farrellys work to puncture and deflate anyone who exploits or capitalizes those people.

Look at how effectively they set up Pat Healy (Matt Dillon) as the film’s villain, using his amiable declaration about how good a person he is—“I work with retards”—as a way to get close to the genuinely selfless Mary. At every turn, they set up Warren (W. Earl Brown), Mary’s developmentally challenged brother, as a force of nature, a good-hearted wrecking ball. Warren earns plenty of laughs in the film, but there’s not a single one where Warren is the butt of the joke. Instead, it’s about the exuberance with which he attacks life, about his boundless energy. Anyone in the film who is unkind to Warren ends up paying for it, and it becomes very easy to judge who someone really is by watching how they react to Warren.

Another part of the secret behind the enduring qualities of There’s Something About Mary is the way they build an ongoing family in their films, both behind the camera and in front. It makes sense. The Farrellys are a family affair, and that’s true of everyone they invite to come play with them on these films. It’s an almost embarrassingly great cast, with Diaz at her very best here. Mary may not be fully aware of the impact she has on everyone around her, but she’s no dummy, and that’s a very hard line to play in comedy. Stiller has to navigate an equally tricky path as Ted, because he does some terrible things in the film. Still, when he’s set next to the characters played by Lee Evans, Chris Elliott or Matt Dillon at his absolute sleaziest, Ted ends up looking like a saint. That’s no accident. The Farrellys, at their best, manage to make blisteringly raunchy films that are sweeter than the sweetest Disney movie, and that inherent kindness that is baked into their work is what buys them permission to push things as far as they do. There are plenty of other people working in the same type of shock comedy, but very few have ever been able to muster the genuine heart of these blue-collar Boston boys.