The fourth installment in the “American Pie” franchise (eight if you count four straight-to-DVD titles) is predictably one-fourth as funny as the original film.

“American Reunion” brings the horny cast together this time for their 13^th-high school reunion. That’s not a real thing, of course, but never mind. We’ve got numerous raunchy sex jokes and just under two hours to get through them all.

The appeal of the series (the theatrical releases anyway) boils down to a few engaging characters. Hapless Jim (Jason Biggs) still gets himself in embarrassing sex predicaments (sexdicaments?), almost none of them very funny, but you have to appreciate how Biggs will do literally anything to top his previous “achievements.”

Lovable scoundrel Stifler (Seann William Scott) can still grab hold of a scene and shake it violently until something funny drops out, and Eugene Levy returns as Jim’s dad to provide some more awkward advice.

The third film, “American Wedding,” smartly eliminated the likes of Chris Klein, Tara Reid and Mena Suvari in favor of a more straightforward story. “Reunion” brings their uninspired characters back and devotes way too much time to rehashed conflict from the first movie. The only entertainment value comes from deciphering the words coming out of Reid’s cigarette voice and watching Klein trying to lift an eyebrow to convey emotion on his rubber face.

We haven’t seen these actors lately for good reason.

There could be a good movie hidden somewhere in this endless array of crude humor and stilted plotting. Jon Hurwitz and Hayden Schlossberg (the “Harold and Kumar” films) hint at real conflict. Jim and wife Michelle (Alyson Hannigan) have lost interest in each other since the birth of their son, and worldly Finch (Eddie Kaye Thomas) hasn’t been completely honest with his friends about his life since high school.

All this real stuff, the perfect fodder for a movie about reuniting with old friends and facing adulthood, is glossed over in favor of poo jokes and fantasizing about barely legal teenagers.

Perhaps it’s unfair to expect more, but there just aren’t enough genuine laughs to give “Reunion” a pass. It even manages to squander a Neil Patrick Harris cameo—a feat previously considered impossible.

The original “American Pie” came out when I was in high school, making me part of the demographic most likely to see and enjoy “American Reunion.” The problem is I don’t think “American Pie” is as celebrated with our generation as the filmmakers want it to be. It was a funny movie that led to sequels with diminishing returns. Just like almost every other movie franchise.

I eagerly await the futuristic installment with the entire cast in old age makeup. If “Reunion” makes enough money, it could happen.

Grade: C