A stable of comic veterans helming a script with Robert De Niro as the star, plus a phenomenal supporting cast, still left the bitter film “The Comedian” with way fewer laughs than the title suggests. On the other hand, the film does not go so far as to render its title ironic; it’s neither black enough nor funny enough to succeed as the black comedy it’s meant to be.

De Niro stars as Jackie, a mean old comedian who is still recognized for a beloved sitcom role, but is currently performing as many profane stand-up gigs as his long-suffering agent (Edie Falco) can scrape up for him. One of the few attendees at his show turns out to be a heckler, who provokes De Niro for the sake of his own web show about heckling comedians. As the heckler’s wife records, the men come to blows, and soon the video is viral and De Niro is in the slammer. After 30 days in jail, he is performing community service and meets Harmony (Leslie Mann), who is doing the same thing.

Every time a new member of the supporting cast pops up, it’s someone incredible. Danny DeVito stars as his brother, and Patti LuPone as DeVito’s wife. Their scenes are almost enough to carry the film. Harvey Keitel plays Harmony’s father, himself an ex-con who also happens to be a controlling dad.

Mann’s usual tartness works well for this role, and her character works well with Jackie. They are genuinely troubled people whose motivations and backgrounds are reasonably well explained.

There are some sequences when Jackie is around his fellow comedians at real locations, such as the Comedy Cellar and the Friar’s Club, when the experience of the writers seeps through and the film becomes real and interesting. One of the co-writers, Jeffrey Ross, is a major Friar’s Club elder statesman, and longtime comedy and Hollywood insiders Richard LaGravenese and Lewis Friedman also co-wrote.

Their expertise casually but completely informs the film in these scenes. It seems we could have gotten a brilliant backstage take on the comedy world from these screenwriters, but the film’s star slows it all down.

It is when De Niro takes the stage and performs his comedy act that things come to a grinding halt and, since this is a movie about him being a comedian, he does so repeatedly. So many films have been made by real comedians about the inner workings of the life of a stand-up comic, but this film stands out because “The Comedian” in question simply is not one. Some just have “it,” and De Niro does not. “It,” apparently, cannot be faked.

In the end, and especially at the actual end of the film when a child delivers a stand-up routine at her school talent show, “The Comedian” is tonally perplexing. I really don’t know who this film is for. We see a geezer getting his mojo back through a form — the internet — with which he isn’t really familiar, so maybe older people would like it, but it’s also incredibly profane. In one particularly painful episode, De Niro addresses a room full of nursing home residents, who are surprised and delighted by his potty humor. If it had actually been funny, we viewers might have been, too.