In the prologue, Annie (Cameron Diaz) blogs incessantly about the spicy sex life she enjoyed with her husband, Jay (Jason Segel), when they met in college, when they first copulated, the second time they copulated and right on up to the time they married and had children (Sebastian Hedges Thomas, Giselle Eisenberg).
Then suburban life -- and exhaustion -- robbed them of carnal pleasure. So she comes up with the idea of sending the kids to Grandma (Nancy Lenehan) overnight, during which time they make a three-hour sex tape, depicting all the anatomical positions in "The Joy of Sex."
After that set-up, it's all downhill. Predictably, the next morning, Jay forgets to erase their vigorous frolic and inadvertently uploads it to the elusive iCloud, where it's distributed via gifted iPads to friends and family. Joined by their voyeuristic pals (Rob Corddry, Ellie Kemper), they try to retrieve the iPads and then, toting their sleepy children along, they break into the San Fernando Valley headquarters of a sex-video website and are caught by the porn broker (Jack Black).
Idiotically scripted by Kate Angelo, Jason Segel and Nicholas Stoller, and sluggishly directed by Jake Kasdan ("Bad Teacher"), it's tame, tepid and terminally dull, never achieving its farcical potential.
Its only redemption comes with the pivotal appearance of Rob Lowe, who, back in 1988, starred in his own, real-life celebrity sex-tape scandal. Here, he plays Hank Rosenbaum, Annie's prospective boss, a narcissistic, coke-snorting toy company CEO whose posh home is filled with paintings of his face superimposed on depictions of Disney cartoons.
As for visual nudity, forget it. Diaz plays peek-a-boo, revealing little, while Segel, who went full frontal in "Forgetting Sarah Marshall," also goes coy.
While Diaz's trim body is enviable, her face looks so Botox'd that it's become a waxy mask, and Segel needs to spend some time toning his torso at the gym.
On the Granger Movie Gauge of 1 to 10, "Sex Tape" is a flaccid 3, frantically trying to combine family-friendly fun with a shallow sexcapade. It's a total turn-off.