Lessons learned from "Waiting," an insanely hilarious and revolting comedy, in the spirit of "Clerks," that examines one long day in the life of restaurant workers: ● Whatever you do, don't send your mashed potatoes back, requesting extra gravy. You don't wanna know what the "extra" is. ● Waiters take tips personally. Undertip, and they may scornfully give the cash back to you with a stiff, "You forgot your change, sir." Overtip, and they might interpret it as haughty condescension. They'll still keep the dough, though. ● You know those clap-happy "Happy Birthday" songs by clusters of waiters? The clappers/singers may be grinning, but they're hating every moment of it. ● Ryan Reynolds is one of the funniest men alive. Written and directed by newcomer Rob McKittrick, the comedy is an example of ace casting, with each character suited to the perfect pitch of his or her character. Set at a bar and grill in the mold of Applebee's or TGI Friday's, "Waiting" probes the alternately sad and amusing plight of gratuity slaves. It's a never-ending battle with bitchy customers, oppressive managers, cooks obsessed with bodily fluids, druggie bus boys and intimidating dishwashers. There's also a running gag in which male staff members trick one another into glimpsing at their genitalia. The dialogue is toothpick-sharp, and the endless comic setups are as rich and caloric as a brownie sundae. McKittrick's most inspired choice was Reynolds, an underappreciated comic actor who owns one of the most electric deliveries around. Reynolds runs away with the film as Monty, a veteran waiter, late 20s, who's seen everything, knows all the angles and has appointed himself the king and jester of the food service set. We've all known guys like Monty, an egocentric man-child ever-ready with a quip, insult or inappropriate blurt of nonsense. He seems eternally stuck in the high school locker room. Whether you're laughing at or with Monty, he's a constant source of exuberant entertainment. He lusts shamelessly after Natasha (Vanessa Lengies), the flirty 17-year-old hostess, who lets him know not so subtly that she'll be 18 in a week. "I guess that doesn't leave me much time," Monty quips. Such jokes may be morally reprehensible, but that doesn't stop them from setting audiences afire with laughter. McKittrick's script is all the funnier because of its shock factor. The writing fears no boundaries and cheerfully stomps all over a sense of common decency, playing as a throwback to the riotous gross-out comedies of the 1990s, such as "There's Something About Mary." One of the keys to the film's success is Anna Faris, who plays Serena, Monty's whip-smart ex-girlfriend, a skilled verbal fencer capable of putting the clown in his place. Chi McBride and Luis Guzmán make up a scene-stealing syndicate as crazy middle-aged backroom workers. David Koechner hits a quirky note as Dan, the buffoonish staff manager who throw his weight around with clueless hubris. Dan also has a thing for Natasha. The audience's entry point is Dean (Justin Long), a 22-year-old suffering a quarterlife crisis. He fears sticking with the job and transforming into Monty. Or worse, Dan. The comedy doesn't stop at the end credits. Following a delicious epilogue montage, the two deadbeat, wannabe gangsta busboys unleash a freestyle rap song that's every bit as vulgar and offensive as everything else in the film, and just as funny. The film is so outrageous and magnetic that you want to go back for a second helping right away. Hold the mashed potatoes.