It’s not writer-director Noah Baumbach’s fault if his movie “Greenberg,” about a guy named Greenberg, makes me wish for a movie called “Zoidberg,” about the friendless, incompetent, vaguely Yiddish, attention-craving crustacean physician from “Futurama.”

In some ways the characters are similar. “Oh, it’s all so complicated, with the flowers and the romance and the lies upon lies,” Zoidberg once lamented, sounding a note that Greenberg might appreciate. Except that Greenberg, as played by a rebarbative and perpetually nettled Ben Stiller, doesn’t seem very capable of appreciation.

Having flown in from New York to skulk around the Los Angeles home of his well-to-do brother (Chris Messina), who has gone abroad, the fortyish Roger Greenberg promptly embarks on an irresolute affair with his brother’s twenty-something personal assistant (Greta Gerwig), an aspiring singer. There is cautionary talk of him having just gotten out of the hospital after a nervous breakdown, and of her having just gotten out of a relationship. There is awkward sex. There is hesitation, recrimination. They don’t seem to know what they see in each other, or in themselves.

Greenberg keeps touching up his mouth with lip balm, as if to stop himself from saying something awful (it doesn’t work), as if his soul itself were the thing that’s really chapped. He announces that he’s “trying to do nothing for a while,” but still makes time to write cranky letters to corporate and political entities that have offended him, and to brood over his fallow creative ambitions. He used to play music, but now he’s a carpenter. He starts building a doghouse for his brother’s dog, but doesn’t get very far.

Greenberg’s way of caring for others tends to consist of inquiring about their opinions of him, with acrimony aforethought. He reconnects with an old flame (Jennifer Jason Leigh, who conceived the story with Baumbach and is his wife), and can’t seem to stand seeing her settle in to motherhood. He tracks down an old bandmate (Rhys Ifans), as if only to reiterate and defend his own reasons for years ago bailing on their record deal. Eventually he finds himself at a house party, feeling threatened by a gaggle of blithe little scenesters who are half his age, and using their coke to embolden his aggression. At one point, while accompanying a woman on her way to an abortion, the kindest thing he can think to say is, “It’s your day.”

This is a fine and self-inverting turn from Stiller, who for once seems not to crave our attention but instead to be burdened by it; and a self-expanding one from Gerwig, who’s made an onscreen habit of involvement with unpromising guys, and has a generously recessive way of suggesting that this movie may actually be about her. “Greenberg” has some kinship with “Annie Hall” — neurotic New York Jew, briefly adrift in L.A., reflects on costs of creative life and past romances, hooks up with beguilingly ditzy would-be singer, boils poignantly and humorously with disappointment — but there’s no mistaking Noah Baumbach for Woody Allen.

Baumbach is as perceptive about aimlessness as he is adept at offhandedness. Whether these gifts are ideally complementary may have to remain an open question. I believe we are meant to admire “Greenberg” the movie because it doesn’t take pains to redeem Greenberg the man. There is bravery in Baumbach’s presentation, but also a sort of self-congratulatory understatement. Again, I think of that other willfully and endearingly repulsive figure, Zoidberg, who once said, “OK, so you’re nonchalant. Stop rubbing our noses in it.”