The film takes its title from the old vaudeville joke in which a comic walks across the stage and encounters a straight man with surprise: `Rappaport! What happened to you?' he says. `You used to be a short, fat man and now you're a tall, skinny man.' `I'm not Rappaport,' says the straight man. And this goes on for a couple of minutes until the comic says, `Rappaport, you used to be so well dressed and clean and now you're dressed in filthy old clothes.' `I'm not Rappaport,' says the straight man. `So you changed your name too!' says the comic.
Nat's most vivid remembrance is that of a meeting when he was five years old in which a passionate woman, Clara Lemlich (Elina Lowensohn), summoned the Ladies Garment Workers Union to participate in a general strike. He is a follower of radical left-wing causes who focuses his remaining energy and considerable wit on helping others facing injustice. Midge doesn't want any part of social activism but, when the spokesman for the tenant's committee threatens to eliminate his job and apartment dwelling, Nat pretends that he is Midge's lawyer and intervenes, making clear that the issue is a society that underestimates and mistreats its senior citizens. In another sequence, Nat pretends he is a consumer spokesman and brazenly marks down the price of meats and groceries in the local supermarket until he is thrown out on his ear.
Things take on a darker tone, however, when a local hood, J.C. (Guermo Diaz) seeks protection money from the elderly. The pair also becomes involved with drug dealer "Cowboy" (Craig T. Nelson) who threatens street artist Laurie (Martha Plimpton) with physical harm if she doesn't pay him the money she owes for drugs. These two episodes are the least effective in the film and do not add much to our understanding of the characters. The most touching sequence, however, is when Nat's schemes are revealed as a desperate attempt to maintain his independence from his daughter Clara (Amy Irving) who wants greater control over his life. While his activities seem harmless, Clara is fearful of her father's visits to the park and wants him to live with her or in a managed care facility. "I'm not going to live in Siberia in Great Neck" with her, he tells her, then makes up a story about a long-forgotten daughter who has invited him to live with her in Israel.
While ostensibly I'm Not Rappaport is essentially a two-man show, in reality Matthau grabs the spotlight and never lets go, reducing Davis' role to film fighting off Nat's outlandish talks and schemes and playing straight man for his comic routines. While the film is a comedy, there is sadness in the fact that a once powerful set of beliefs is now reduced to pathetic gestures by sentimental old men. Even when Gardner pays tribute to the Jewish tradition of social action, the Bolshoi Chorus belting out the Internationale seems to mock their passion. For these men, old age does not bring security, status, or emotional fulfillment, only longing for the society that might have been and the men they could have become. For them, there is little left to cling to except a wistful kind of grace.