A snakes−in−the−grassroots geek−out on the Internet has made anyone opening a Web browser since late 2005 aware of the movie Snakes on a Plane. The online flood of responses to such a movie’s potential even inspired its studio, New Line, to beef it up with more blood, bad words and booty to an R−rating.

You’re no doubt wondering: All this for a story about a U.S. marshal (Samuel L. Jackson) trying to save a murder witness and frightened passengers on a plane beset by scores of poisonous snakes ready to slither into the buffet line?

Should you take that dismissive tone with Sam the Man, well, paraphrasing Pulp Fiction, allow him to retort. One official marketing scheme from New Line was allowing people to send “personalized calls” from Jackson to their friends. Part of his spiel was that Jackson knew it sounded crazy, but he thought Snakes on a Plane might very well be the greatest movie ever made.

Not quite, but its B−movie nirvana of stupid−goodness is unmatched by anything else with the full support of a studio, and it’s easily 2006’s most entertaining film — primal at every level, from the basic fears it exploits to the roaring reactions it elicits, whether they’re howls of humor or horror.

The yelping makes Snakes on a Plane the only movie in more than three decades that, without qualification, must be seen in a packed theater to be enjoyed. Those arguing against at-home viewing and for moviegoing as a continued communal experience just got an unlikely new ally. Everyone, including me, has said of some film that you should you see it on the big screen. That is shorthand for beautiful cinematography, great sound or wowing visual effects. A movie can lose something on a 20−inch TV that it otherwise has on a 50−foot screen, but most are great or awful however they’re watched.

Not the case with Snakes on a Plane.

Attend a 4:10 p.m. matinee on Wednesday, and you’ll wonder what the hell I’m talking about.

At 10:20 p.m. Saturday, it will be the most ridiculously fun 105 minutes you’ve had in a theater.

That certainly was the case at last Thurday’s advance screenings of the film — the rare case of a studio wisely holding off on showing it early for critics and contest winners. I was but one of a hoot−and−holler crowd cheering, clapping and laughing its butts off at Snakes on a Plane‘s uncanny balance of cheese and seriousness. Never before has a movie−theater vibe been so delightful to take in.

People wore T−shirts, draped rubber snakes over their shoulders and even had audience−participation lists a la The Rocky Horror Picture Show — the last movie prior to Snakes on a Plane that absolutely, positively must be seen in a theater to be fully appreciated. Anyone who, like me, first viewed Rocky Horror on VHS in 1990 understands why it took 15 years to hit home video: After the first hour, it’s a lifeless slag with an interminable drag. Without costumes, confetti, bells and toast (unbuttered to avoid a mess, mind you), it’s a phenomenal bore. Sadly, it will be the same with Snakes on a Plane if you wait until its Dec. 5 DVD release to find out what the hubbub is about.

If New Line is smart, it will bump it back to be ready in time for Christmas of 2021, if ever.

No movie with an eight−figure budget released to 3,555 theaters can ever be called a cult classic; with the Internet, can anything? With Snakes on a Plane, New Line could usher in what would be known as the mainstream midnight movie. The same idea already is in play for Feast, the oft−delayed Project Greenlight horror flick set for late−night screenings across America on Sept. 22 and 23. (Of course, a quick DVD scuttle in October is planned for that, too.)

Snakes on a Plane perhaps is not an every−weekend success in perpetuity a la Rocky Horror, but if handled as a rare treat, it will be a kitschy event for years. A handful of prints, weekends only, the later the better. The 5−year−olds tucked in by a sitter while Mom and Dad saw Snakes on a Plane last weekend (when it made $15.2 million) should get the chance to feel the same rush as college freshmen.

Come on, New Line − don’t dream it, be it. Besides, the living room just won’t be as fun a venue for my friends and I to shout “Whoo!” as the Chinese mobster swings his bat, ring a bell during the microwave scene or wear our freshly minted “That’s all you talk about, Troy!” T−shirts.