If “The Wedding Crashers” were a woman, it would be the kind of female that the two main characters, John (Owen Wilson) and Jeremy (Vince Vaughn) hate — a tease.

Beautiful and occasionally funny, but spends your whole time together leading you on with seductive promises that ultimately go unfulfilled. The movie, in the words of Jeremy, “never seals the deal.”

“Crashers” begins promisingly with the two main Lotharios embarking on another wedding season. You see, John and Jeremy don’t like marriage or commitment, but they love to sleep with beautiful, vulnerable girls. They chart out 17 weddings that they plan to crash and adopt pre-planned backgrounds in order to fit in with the families. They pretend to be Irish, Jewish, Italian and Indian: whatever it takes to get inside.

We see the boys having the time of their lives cracking jokes with the old timers, making balloon animals for the children (always making sure a beautiful woman sees the good deed) eating delicious wedding food and dancing.

It ultimately ends with a music montage featuring the wedding staple, “Shout” by Otis Day and the Knights alternating between reception fun and them taking beautiful women to bed with them.

After wedding season is over, John does a little soul searching, saying they aren’t old, but maybe they are too old to be doing this. Jeremy has other ideas, and convinces his buddy to crash “the Kentucky Derby of weddings,” the nuptials between the daughter of Treasury Secretary Cleary (Christopher Walken).

The boys each fall for a different Cleary daughter. John falls for Claire (Rachel McAdams) because she is smart enough to realize how stupid the wedding is. Jeremy falls for Gloria, played by Isla Fisher who completely steals the show with her brilliantly psychotic performance, because she is beautiful and tossing him seductive glances. Gloria turns out to be a “stage 5 clinger” and falls in love with Jeremy after they sneak away and have sex. Jeremy knows through the rules of wedding crashing (there are hundreds) that he needs to leave and leave now. But John needs more time to “seal the deal” with Claire. They wind up at the Cleary vacation home for the weekend pretending to be venture capitalists.

This sets up a brilliant premise that the film just can’t execute to its fullest potential. The film is intermittently hilarious, no doubt. But it shows us so much potential for more and doesn’t deliver. Vaughn and Wilson have terrific chemistry together and play off of each other effortlessly. Vaughn’s neurotic fast-talking wiseguy and Wilson’s breezy, easygoing charm match perfectly. But the two seem as if they don’t have confidence in their material, but with confidence that they can make any material funny.

Some of the time they are right and the film has a number of gut-busting laughs throughout. But when they are wrong, it is painful to behold. Some jokes fall so flat that it ruins the flow of the movie, and the silence becomes deafening.

The film has a hodgepodge of crazy characters for John and Jeremy to interact with at the Cleary home, but completely forgets about them once they leave the screen.

There is the Cleary teenage son who is an outcast homosexual artist, a foul-mouthed old grandmother, an adulterous wife and a sadistic boyfriend. Each character has the potential to be very funny, but the movie gives them each a scene to show just how crazy they are and doesn’t give you anything else.

The film may know all the rules of crashing weddings, but it doesn’t know many of the rules of comedy. Rule one is when you have the always hilarious Christopher Walken: use him. The movie doesn’t give him a single line of funny or memorable dialogue. Rule two is when your movie is pushing two hours in length, the weakest part can’t be the third act. Into the third act the movie chugs along towards forced sentimentality that doesn’t fit the refreshing raunchiness of the beginning.

Will Ferrell shows up towards the end as the godfather of wedding crashers who has moved on to crashing funerals while still living in his mom’s basement. Though he steals his scenes, he can’t completely save the movie.

Ultimately it’s a shame. For a movie that promised to be a throwback to the R-rated comedy heyday of the 80s, the film is nothing more than a tease of what could have been a brilliant movie.