UNSCREWED

½ (two and one half stars)

Sex is funny.

Running time: 75 minutes. Not rated (sexual situations and language, brief nudity). Playing at the Quad Cinema, 13th Street, between Fifth and Sixth avenues.

WHO doesn’t giggle at words like “tantric yoga” and “dildo”?

And tell me you wouldn’t snicker at a man standing nervously in a hospital robe as his doctor dips a gloved finger menacingly into a pot of KY Jelly.

That’s rich (if well-plowed) comic soil, and a New York improv troupe called the LabRats makes hay with it in their low-budget indie movie “Unscrewed,” which was produced for peanuts (and looks it), but offers enough laughs to please even those who don’t usually venture into downtown art houses.

The film is a “Waiting for Guffman”-style mockumentary about a married couple on a quest to spice up their love life with help from various sexperts, including a psychiatrist, a urologist (that’s the one with the KY) and a trio of tantric yoga teachers who clang cymbals, burn incense and encourage the couple to strip for each other.

The actors are all members of the LabRats, as well as veterans of soap operas and various off-Broadway shows. They helped write the script through months of improvised rehearsals.

As in “Guffman” and other improvised comedies, a big part of the fun is the way the actors play everything deadpan, making the most earnest faces as they fiddle with rabbit-shaped vibrators.

Some of the straight-faced humor falls flat. A couple of scenes in the psychiatrist’s office are just plain boring, as the silences stretch on awkwardly and the therapist says, “How does that make you feel?”

Other moments are funny enough to make it on Larry David’s “Curb Your Enthusiasm” – like when the psychiatrist suggests some “replacement therapy,” which consists of him getting into bed with the wife and playing the part of her husband.