“Old School,” the thirty-something wannabe “Animal House” for the new millennium, is a smelly, dilapidated eyesore of a university frat house: peeled, chipped, vomit-colored paint; poorly constructed, sagging porch; mangled screen door resting on one hinge; crude, offensive photographs of drunk female “conquests” in the front hall; ever-growing puddle of keg beer in the back room; and the sticky floor that leads to nervous contemplation of why it’s sticky.

Despite the disgust such a residence elicits, it undeniably demands a level of grudging respect as well: It is so simple, so unapologetic, so shameless. It exists only as a means to achieve horny, drunk, sophomoric and often very funny late-adolescent rabble-rousing.

With that said, “Old School,” directed by “Road Trip” creator Todd Phillips, is certainly no “Animal House.” The story centers on three best buddies in their early 30s who have all reached a crossroads in their lives. Mitch (Luke Wilson) has recently broken up with his excessively sexually adventurous girlfriend Heidi (Juliette Lewis). Beanie (Vince Vaughn) is a husband and father uncertain about the predictable routine he has settled into. And Frank (Will Ferrell) recently married his longtime girlfriend Marissa only to suffer anxiety over the “responsible adult” categorization such a union signals.

This trio of maladjusted men takes the only natural course of action: They turn Mitch’s new on-campus house into a fraternity, enlist a ragtag band of members ranging from a timid young college student to an elderly retired military man, and they throw a series of wild keggers. In short, unable to deal with their lost youth, they decide to find and rehabilitate it. And in the process, they — for the most part — come to grips with the responsibilities of adulthood.

It is a waste of space for any “Old School” reviewer to obsess about the technicalities of film construction. Yes, the story is at times ridiculous and moronic. Yes, this type of gross-out humor is a current Hollywood staple. Yes, many of the side characters — especially the antagonistic school dean played by Jeremy Piven — are one-dimensional college comedy cliches. Anyone who harps on such flaws should be quiet and go see “The Pianist.”

Here’s the bottom line: “Old School” is undeniably uproarious entertainment. It is less a coherent film than an anthology of gut-busters loosely strung together under the tone of frat boy immaturity. What does an all-female blow job class really have to do with the guys’ fraternity endeavor? Nothing, but it’s funny watching an effeminate Andy Dick share oral wisdom in a disturbing red-brown wig. Because of this “cram any funny idea into the movie” attitude, “Old School” never reaches the subtle yet zany and irreverent brilliance of a classic like “Animal House.” The sad truth of today’s youth comedy market is that such a cult achievement may be too much to hope for.

While lacking the inspiration of legend, the movie still presents a diverse buffet of mindless comic bliss. The vast majority of these silly moments belong to recent “Saturday Night Live” alum Ferrell, who could not have made a better choice than to leave that sinking ship. In “Old School,” Ferrell plays the blank-faced misfit to near perfection. His comedy falls out of nowhere like a snake dropping from a tree: One moment he is all calm understatement and the next he is over-the-top hysteria. When Ferrell does unleash his perfectly modulated explosiveness, he does so with masterful timing to maximize the giddy impact of the surprise.

Between the remaining two headliners, Wilson plays the straight man a little too straight at times, but he is the glue that holds the ensemble together. Vaughn is back in fine “Swingers” comic form after a bizarre, extensive foray into drama. (What bonehead told him starring as Norman Bates in a shot-by-shot remake of “Psycho” was a smart career move?) He unearths a few gold nugget bits, particularly the way in which he protects his young son from profanity.

Beyond their individual performances, the three actors have a natural, seamless onscreen chemistry. It is that unity, the ability to play off one another and set each other up for the spike, that separates good comedies from bad ones. No matter what state the frat house is in, if the people who inhabit it are a fun, rowdy, well-matched bunch, you can have a good time even if the ceiling is falling in around you.