"Earmuffs!" Cover your ears if you're too young, but if you're of a certain age, you'll be astonished to hear that it's been 15 years since "Old School" enrolled at the multiplex.

Released on February 21, 2003, the modern-day answer to "Animal House" made Will Ferrell into a bankable movie star, put future "Hangover" director Todd Phillips on the raunchy-comedy map, helped coin the phrase "Frat Pack" to describe the loose brotherhood of movie comedy stars that included Ferrell and Vince Vaughn, and introduced a variety of bizarre hazing rituals to American college fraternity life.

Like midterm exams, "Old School" keeps reappearing, at least in rotation on cable. Still, as often as you've watched it, there's much you may not know about the college comedy. So read on and study carefully; there may be a pop quiz later.

1. "Old School" was actually Phillips' third movie about hard-partying college students. The first was his 1997 documentary "Frat House." Phillips took that movie to the Sundance Film Festival, where he met fabled comedy filmmaker and "Animal House" producer Ivan Reitman. Reitman turned Phillips toward comedy and produced his next two films, campus farce "Road Trip" (2000) and "Old School."

2. The idea for a movie about three early-middle-aged men trying to return to their irresponsible fraternity days came from Phillips's friend, ad man Court Crandall. He earned a story credit on the film, though the final screenplay was written by Phillips and his writing partner, Scot Armstrong.

3. Armstrong and Phillips wrote the part of Bernard with Vaughn in mind, having been impressed by his comic performances in movies like "Swingers" and "Made." But Vaughn had done such a good job of establishing himself as a serious dramatic actor that the studio didn't want him for "Old School." "They didn't think I could do comedy!" Vaughn marveled in 2015. "Todd really had to push for me; I think he even told them to watch me on Letterman, to see that I could be funny."

4. That's Phillips, by the way, playing the guy who knocks on Luke Wilson's door early on and says, "I'm here for the gangbang."

5.Patrick Cranshaw had been acting in films for 50 years before "Old School," but it was his role as lube-wrestling frat brother Blue that finally made him famous at age 84. He died three years later, but not before hearing countless fans greet him with Ferrell's line, "You're my boy, Blue!"

6. The three leads (Wilson, Vaughn, and Ferrell) teased each other on set. Wilson recalled Ferrell telling him he was sorry he hadn't yet seen Wilson's performance in "Legally Bland." Wilson shot back with a warning that "you might just want to keep one foot back in TV just in case this whole movie thing falls through."

7. The house that Wilson's friends transform into the home of their new fraternity is a real residential house located on Pasadena's Bushnell Avenue, on a two-block stretch that has been used for locations in several Michael J. Fox movies. The same house appeared in "Back to the Future Part II" (Biff steals a kid's ball and tosses it onto the house's balcony), while down the street are George McFly's 1955 home from the first "Back to the Future" and the house where the 1955 Lorraine lived in that movie -- a house that was also where Fox's character lived in "Teen Wolf."

8. The college scenes were largely shot in Los Angeles at UCLA and USC. There's one helicopter shot of the campus, however, that may look familiar. It's actually flyover footage of Harvard University, which Phillips recycled from "Road Trip," though no ground scenes in either film were shot at the Cambridge, Massachusetts campus.

9. Who's the wedding singer who inserts subliminal profanities into the lyrics of Bonnie Tyler's "Total Eclipse of the Heart"? It's Dan Finnerty of The Dan Band, an act that became the toast of Hollywood nightclubs by performing a repertoire of songs made popular by female singers. A comic who's married to Kathy Najimy, Finnerty would perform similarly inappropriate songs in Phillips's "Starsky & Hutch" and "The Hangover."

10. Also, the church where Ferrell gets married showed up again two years later in Vaughn and Owen Wilson's "Wedding Crashers."

11. The last day of the shoot was devoted to the Mitch-a-Palooza party, the one that starts with a surprise performance by Snoop Dogg and ends with Ferrell streaking through town. Ferrell had already shot the streaking sequence -- and yes, he ran naked for real, apparently horrifying local lookie-loos who had no idea they were going to be treated to full frontal Ferrell -- but he needed some liquid courage to drop trou in front of the rap icon. "To actually be in front of Snoop Dogg that close naked," Ferrell said, "that was more intimidating than anything."

12. Snoop Dogg so wanted to play Huggy Bear in Phillips's upcoming adaptation of "Starsky & Hutch," that the director was able to persuade the rapper to cameo as himself in "Old School" as a condition for landing the role he coveted in Phillips' next movie.

13. After his scene was complete, Snoop summoned Vaughn to party in his trailer. Wilson was miffed to find out about the revelry later; apparently, no one had invited him.

14. The budget for "Old School" was reportedly $24 million. It made back $76 million in North America and another $11 million abroad.

15. "Old School" not only made Ferrell a breakout star, but it also led to the coining of the term "The Frat Pack" to describe the group of comic actors and frequent collaborators that included Ferrell, Vaughn, Luke and Owen Wilson, Ben Stiller, Jack Black, and others.

16. In 2006, Armstrong wrote a script for a sequel, "Old School Dos," that would have sent the trio of aging frat boys on spring break. Ferrell and Vaughn nixed the idea as being too much of a retread. Wilson, however, was game, though he said he understood Vaughn and Ferrell's position. "As funny as those guys are, they are pretty damn thoughtful and would hate to squander the goodwill of the first one with one where it just seemed like the studio was just trying to cash in."

Indeed, in 2016, Wilson was still game, saying, "I, of course, would do it at the drop of a hat."