“The Comedian” has been billed as Robert DeNiro’s passion project, starring DeNiro himself as the aging television star Jackie, who is desperate to reestablish his stand-up comedy career. After getting physical with an audience member during a show, Jackie is sentenced to community service, during which he meets the equally down-on-her-luck Harmony (Leslie Mann). The two form a kinship as he tries to revive his career through vile stunts, television pitches and high-profile comedy shows.

If that synopsis seems a bit thin, it’s because the film lacks much of a plot. There are plenty of subplots, including a romance between Jackie and Harmony, Jackie’s relationship with his estranged brother (Danny DeVito) and his attempts to start a family, Harmony’s relationship with her father — who might be a mob boss — and Jackie’s various stunts to regain stardom. Honestly, “The Comedian” works best when it doesn’t have a main story. Its loose, relaxed vibe works to tell this story of an aged icon. The various actors play off each other with a welcome casualness, and a slick jazz score evokes a neon-tinged vision of New York that tonally feels just right.

However, it’s also the lack of plot that makes almost everything else forgettable or downright infuriating. Like many passion projects or star-driven comedies of this decade, this film allows its stars extended improv sequences that quickly overstay their welcome — an unfortunate side-effect of directors and editors too afraid to tell their stars to tone it down a bit.

The second half of the film takes a detour into a Florida retirement home, where the tone and style hit a brick wall. The humor — which fluctuates throughout the earlier part of the film from raunchy and funny to endless and gross — nosedives into tasteless and exhausting. The subplots begin to hog air time that could have been better spent with Jackie, his agent or his brother, who are supposed to be the stars of the show.

What ultimately sinks the whole affair is the romance between Jackie and Harmony. It starts out endearing and cute, with the two sharing a subtle and playful chemistry. But as the plot devolves, the nature of their relationship becomes overdone to the point of disgust. Initially, the pair feel like Rocky and Marie from the classic “Rocky Balboa.” “The Comedian” reinforces why that particular couple never got too intimate. Ultimately, Jackie and Harmony’s relationship becomes the driving force as a twist takes the film in an unthinkable direction, sinking whatever charm or grace this messy narrative had previously created.

It’s never fun to criticize a passion project, especially one of a renowned artist. To think that DeNiro spent a portion of his time, energy, drive and clout to develop this film, only to have it fizzle out is honestly a bit depressing. But “The Comedian” is a sloppy, unorganized waste of potential that might be insulting if it were worth remembering.

Email Carter Glace at [email protected].