Don Jon: a love triangle between a woman, a man and his laptop

Joseph Gordon-Levitt and Scarlett Johansson star

In 1964, Supreme Court Justice Potter Stewart famously said that pornography was hard to define, but "I know it when I see it." Jon Martello, the title role of Joseph Gordon-Levitt's candid comedy Don Jon, sees pornography practically everywhere, from sexed-up TV commercials to hardcore Internet clips, and he isn't the type of guy to say no to temptation.

Starring, written, and directed by Gordon-Levitt, Don Jon presents a romantic triangle between a woman, a man, and his laptop. A bartender nicknamed "Don Jon" for his prowess as a nightclub pickup artist, Jon looks like the very model of a New Jersey alpha male. He's got the confident swagger, the muscle car, the jacked-up body with pecs so defined, he has the chest of an action figure.

But Jon also has a porn habit that's so deep-seated, he takes less satisfaction in hot hookups than he does in his alone time with his computer and box of tissues. He admits that even his desktop's power-up chime can get him aroused, and throughout the film the sound becomes a Pavlovian bell that turns on Jon while getting a laugh from the audience.

For a while it seems that Jon could alternate between real women and the pixelated variety indefinitely until he meets Barbara Sugarman (Scarlett Johansson), a bombshell in a red dress and pink lipstick who likes the sleeveless Casanova but resists his advances to go all the way.

Barbara pressures Jon to improve himself by taking a night class, where he meets Esther (Julianne Moore), an older student prone to inappropriate weeping and sly revelations. Esther reveals that she knows a thing or two about pornography, and we believe her because she's played by the same actress from Boogie Nights and The Kids are All Right.

Don Jon makes an amusing joke comparing Barbara's reactions to a Hollywood rom-com with Jon's responses to clips from PornHub. She strongly disapproves of pornography, though, so Jon tries to keep his compulsion under control. At one point, as they fall in love, Jon wanks to her Facebook photos — which could count as progress, maybe? He finds quitting porn harder than he imagined, and when he goes to his laptop on one night, people at the screening I attended were saying "Don't do it!" like Jon was a hapless horror movie character.

Unfortunately, nearly all of the supporting characters are small and one-dimensional. Glenne Headly and Tony Danza play Jon's uncouth parents in light, amusing lunches that convey the character's origins. But like the scenes with Jon's bros, the moments play almost entirely on a sitcom level. Even Johansson gets upstaged.

Gordon-Levitt makes an exception with Jon and Esther, whose scenes play in a much more naturalistic key. Their exchanges breathe, feeling more spontaneous and unguarded, exploring a friendship that seems superficially unlikely, yet somehow inevitable. Gordon-Levitt could have presented the whole of Don Jon in this realistic light, and while it may not have been as funny, it would've been warmer. The differences between the film's two kinds of scenes are quite striking: You'll know it when you see it.