Did you hear the one about getting married and having a family? When you get married and have children, you no longer get to have sex. This basic knowledge has become such a tired movie cliche that it fits snugly somewhere between "a professor gives a lecture about a subject that spells out the theme of the film" and "a grizzled detective gets suckered into one last case two days before retirement." And yet entire films continue to be built around it, including 'Sex Tape,' the new film that reunites 'Bad Teacher' director Jake Kasdan with his stars Cameron Diaz and Jason Segel -- a combination that should make for easy entertainment, but instead lends itself to exasperated groans.

In recent years, we've seen couples experience married-life crises in middling films like the Tina Fey and Steve Carell comedy 'Date Night,' the Meryl Streep and Tommy Lee Jones dramedy 'Hope Springs,' and Judd Apatow's 'This Is 40.' Not even the typically reliable Apatow could make a mid-life marriage crisis entertaining. Conventional wisdom holds that when you get married and pop out some kids, you might as well have just sent your sex life off with a Viking funeral. Our parents tell us this. Our grandparents tell us this. Movies and TV shows tell us this -- we get it.

Early on, 'Sex Tape' recognizes the comedic value in Diaz and Segel trying and awkwardly failing to reignite their old sexual flame -- it's been so long since they've really touched each other that it seems they've forgotten how. But like its predecessors, it unfortunately falls into a melodramatic and entirely unentertaining trap because happily married people in movies are just so ... boring. They have a nice house, they have great kids, hilarious friends like Rob Corddry and Ellie Kemper, and fantastic jobs. Diaz's Annie is a mommy blogger on the verge of selling her blog to a major corporation that makes products for babies and children, while Segel's Jay works at a radio station that affords him luxuries like so many extra iPads that he can give them away as Christmas gifts. If you've seen a Nancy Meyers film since the 90s, you know how hard it is to empathize with these people when their kitchen has marble flooring.

If the biggest problem a married couple faces is a lack of spontaneity ('Date Night') or a lack of sex ('Sex Tape'), it's hard to relate. The people in these films make more money and live better than their on-screen jobs should allow. They are all white, upper middle-class, and drive SUVs. You will not see a film where a less-privileged couple -- living from paycheck to paycheck in a studio apartment and struggling to pay rent -- complain about how their sex life is evaporating because they got married and had some babies. They would not have babies ... because they cannot afford them. They would have plenty of sex because it's a free form of entertainment, and they are too broke to get out much.

The driving conflict of 'Sex Tape' is, of course, the titular sex tape which Jay and Annie make and which Jay unwittingly shares with everyone he's ever gifted with an iPad when he syncs up with the Cloud. When 'Sex Tape' is smart, it focuses on the calamitous humor of an out-of-practice couple trying to have sex for the first time in a long while, and is incredibly sex-positive, even going so far as to point out that there's nothing for Annie to be ashamed of in participating in her own sex tape. When it's dumb, it goes for animal abuse and toilet humor, and makes a recurring joke about the Cloud -- the latter of which firmly reinforces 'Sex Tape' as a film about mundane first world problems. And when it's boring, it's just a couple of married people going through the tired, movie-marriage motions of bickering and bonding over mutual conflict and finding that what they really needed was one crazy night to remind them that they still like each other.

Like the existence of sex tapes, this one peaks with the appearance of Rob Lowe. Lowe plays Hank, Annie's potential new boss, who just so happens to have been given one of the troublesome iPads. There's an extended sequence at Hank's swanky house where Lowe does what he does best, hijacking the film as an overly-positive and exceedingly quirky CEO. His choice in decor is truly exceptional, and the reveals in this scene are vastly more hilarious than the surprise cameo near the end of the film.

'Sex Tape' doesn't tell us -- or its characters -- anything we didn't already know. Marriage is hard, sex is less frequent after you have kids, and sex tapes are always a bad idea. See also: 'Date Night,' where marriage is hard and intimacy is scarce when you have kids, and 'Hope Springs,' where marriage is hard and the sexual spark only gets harder to reignite as you enter old age, and 'This Is 40,' where marriage is hard and, well, you get the idea. The problem isn't that there aren't people who can't relate to these issues, but that for most of us, there's nothing exciting or new or interesting about these ideas. Like Jay and Annie, these movies need to really spice things up -- or maybe just don't press record.

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