Robert De Niro and Leslie Mann attend a wedding in "The Comedian."

Funny people are delightful to be around, but professionally funny people can be exhausting. They turn every conversation into a wisecrack, a pun, an excuse to riff on that thing people do on Facebook. Someone who can relate to the world only via setup and punchline eventually wears you down.

However, how much more exhausting is it to actually be that professionally funny person, especially one who’s successful enough that adoring fans come up to you and expect you to be on, even at a funeral or in the middle of a cheeseburger? The biggest accomplishment of The Comedian is the way it captures both those kinds of exhaustion, and it imparts a certain charm to this inconsequential but insightful drama about funny people.

Robert De Niro portrays Jackie Burke, né Jakob Berkowitz, a foul-mouthed and foul-tempered insult comic based in New York. Once the star of a beloved 1980s TV sitcom, Jackie is now a solitary creature scraping a living at third-tier gigs. An altercation with a heckler gets him sentenced to community service at a homeless shelter, where he meets Harmony (Leslie Mann), who’s serving her own sentence for assaulting her cheating husband.

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This movie is best when it interacts with the world of comedy. Jackie’s stand-up material is pitched perfectly: funny but not so funny that you wonder why he isn’t a bigger star and raunchy enough that a younger, Judd Apatow-steeped crowd might plausibly laugh at his jokes. His barbs at the audience come from a place of deep insecurity, which Jackie naturally flaunts onstage. I like the way De Niro bends over at the waist and covers his face while reciting Jackie’s inner monologue into the mike: “These people came to see you! What are you doing? Don’t insult them! Don’t curse so fucking much! Don’t say the n-word!” His gift also lets Jackie improvise a way to piss off Harmony’s overbearing dad (Harvey Keitel) when he meets him.

Old-hand director Taylor Hackford (Ray, An Officer and a Gentleman) should have concentrated on that, but instead he lets this overstuffed script pad this movie out to 121 minutes with cameos by De Niro’s co-stars from other movies and stand-up comics portraying themselves (Billy Crystal, Hannibal Buress, Brett Butler, Gilbert Gottfried). The seeming career breaks that Jackie catches — hosting a reality show, roasting a comedy legend (Cloris Leachman) — aren’t funny enough in themselves, nor do they shed light on the character or his milieu. The relationship that develops between Jackie and Harmony attempts to introduce some unpredictability into the script, but it doesn’t come off.

No, this movie and a livelier-than-usual De Niro do their best work examining the impulses that drive people into comedy. You feel Jackie’s simple, addictive joy at making a room laugh when he does an impromptu set at a Florida retirement home. When Jackie’s niece (Lucy DeVito) begs him to say a few words at her lesbian wedding, his tendency to work close to the edge with jokes about incest and semen makes you wonder if he’s going to say the wrong thing that will blow up the only family connection he has left. At such times, The Comedian touches the dangers and thrills of the world’s funniest profession.