Robert De Niro stars as Jackie Burke, an aging comic icon who has seen better days. Despite his efforts to reinvent himself and his comic genius, the audience only wants to know him as the former television character he once played.

Tragically unfunny, “The Comedian” reminds us that not even great actors can knock one out of the park every time.

Despite a talent pool of A-list players accomplished in film, TV and stage, this crude, crass, lowbrow comedy has a title that seems bracketed by irony quotes. Burdened with a choppy, poorly conceived script, “The Comedian” is impossible to enjoy on any level whatsoever.

Robert De Niro acquits himself adequately as New York City insult comic Jackie Burke. But given his history of slumming in a dead zone of humor with bombs like “Bad Grandpa,” “The Family” and “The Adventures of Rocky and Bullwinkle,” it seems an especially unfortunate career choice.

Jackie, a sitcom star of yesteryear, has returned to his roots as a stand-up foul-mouth, struggling to adapt to a new world where YouTube exposure can turn nobodies into overnight icons. Performing at half-empty comedy clubs after a decades-long slump, he draws attention more as a nostalgia-infused celebrity than a modestly gifted talent past his prime. Most people call him “Eddie,” the name of his rambunctious TV character 30 years before. Everyone asks him to repeat his lowbrow signature line from the series, a self-referencing nod to De Niro’s own “You talking to me?”

Sarcasm is Jackie’s default form of communication onstage and off. With little money saved from his glory days, he needs whatever work his agent (Edie Falco) can scrounge up. Still, he’s incorrigibly rude to her and virtually everyone else he encounters, treating the world like a random collection of hecklers.

It’s tough to find much reason to have a rooting interest in his comeback bid, especially after he’s sent to jail for beating up an interrupting member of the peanut gallery. It’s even harder to believe he’s desirable enough to win the attention of Harmony (Leslie Mann), a much younger woman with whom he begins an unconvincing romance after his release.

Jackie is presented as a top-notch shock comic who hits audiences with edgy insult jokes like a flamethrower. His material is R-rated for sexual references; in terms of entertainment value, it would be a C-minus or D-plus. De Niro’s talents as a straight man in screwball comedies are impressive, as “Mad Dog and Glory” and “Wag the Dog” proved beyond doubt. But cast as a laugh-riot performer, he gives birth to broad comedic caricatures.

Less wacky than it aims to be, the movie gets what fun it can from a supporting cast of distinguished veterans. Danny DeVito makes a feast of his scenes as Jackie’s deli-owner brother, Patti LuPone carries a molten core of anger as his spiteful sister-in-law, and Harvey Keitel goes full-throttle as Harmony’s bulldozer of a father who is aghast at his daughter’s June-December tryst.

Charles Grodin is credible as a successful comedy warhorse who steals Jackie’s material, but his appearance puts this film in unflattering contrast to his far better work with De Niro in the road trip crime comedy “Midnight Run.” Cloris Leachman has a walk-on role as an aged star whose exit is played as a gag that’s rather grim in light of recent events.

The film hits rock bottom when Jackie visits a Florida retirement home and tickles the old fogies with Irving Berlin’s “Makin’ Whoopee” reworded into “Makin’ Poopie.” The elderly extras guffaw and applaud his swaggering performance in artificial delight. The film’s audiences are more likely to cringe at the spectacle of De Niro, once the most important actor in American cinema, hamming it up in a worthless paycheck role.

He deserves better than this. So do we.