In ‘Don’t Think Twice,’ Birbiglia improves on improv

From left: Tami Sagher, Gillian Jacobs, Kate Micucci, Mike Birbiglia, Chris Gethard, and Keegan-Michael Key in “Don’t Think Twice.’’Jon Pack

“Don’t Think Twice” is comedy inside-baseball, and it’s pretty delicious even if you’re one of those people who ranks a night out watching an improv troupe just above death by mime. The movie’s a gentle farce about that most thin-skinned and self-serious of human subspecies — the professional comic — and it comes to us courtesy of writer-director (and veteran stand-up comedian) Mike Birbiglia. Shrewsbury’s own, he has delivered a sophomore movie that’s leagues above his 2012 debut, “Sleepwalk With Me,” and positions him as a sly observer of our better and worse selves.

Birbiglia plays the pivotal role of Miles, who has been the mainstay of the tatty but proud New York improvisational comedy troupe The Commune for more years than has been good for him. Gaining fast on 40, he lives like a college student and continues to date the more impressionable students in his improv class. It’s not wearing well.

True to its name, The Commune is a six-member cadre of equals, some more equal than others. The group has had a good run with their weekend audiences gamely throwing out suggestions for the cast to riff on, but one night a rep turns up from the hit TV sketch show “Weekend Live” — it’s essentially “Saturday Night Live” with the name changed so Birbiglia won’t get sued — and suddenly the group’s brashest member, Jack (Keegan-Michael Key), is one of the anointed. He’s tapped for an audition and then invited to the big time; in baseball parlance, he has made it to the Show. The others cheer his success and privately seethe.

In fact, the comedy of “Don’t Think Twice” — and it’s an often brutally funny movie — rises from a paradox. The same insecurity that fuels these people’s onstage talent, fast thinking, and ability to get laughs without a net also makes them passionately envious of each other’s successes. Jack’s big break throws the orbital balance of The Commune out of whack: Miles hopes to piggyback into the “Weekend Live” offices as a writer, and so do the troupe’s most shyly eccentric members, Bill (Chris Gethard) and Allison (Kate Micucci). Lindsay (Tami Sagher), a rich girl who the others secretly judge for not having to struggle for rent money, has her own irons in the fire.

And then there’s Sam (Gillian Jacobs), Jack’s girlfriend and troupe-mate. Invited to audition for the show with him, she finds a way to back out, then spends the rest of the movie gnawing over her aversion to fame. Is she worried she’ll fail on a bigger stage? That she’ll become a sell-out? Is it that she simply prefers the direct connection and instant high of the small time? Jacobs, who wielded a sharp edge on TV’s “Community,” softens her approach and gets us to buy into a somewhat unbelievable actor’s dilemma.

Birbiglia keeps the jokes caustic and sometimes in dreadful taste; he knows that working comics push the envelope hardest when they’re among themselves, even when it involves a dying parent. Yet “Don’t Think Twice” manages the neat trick of remaining sweet-natured while letting absolutely no one off the hook. That includes Jack, who Key plays with the charisma of a natural star (he would know, as the costar of “Key & Peele”) and a born glory hound. It also includes the Commune’s paying customers, who stop the improv in its tracks to demand Jack do his signature “Weekend Live” character.

And it includes, with a spiky but loving embrace, every desperately ambitious entertainer who has ever sucked up to a star. In one of the more cringingly funny scenes, “Don’t Think Twice” brings on Ben Stiller as himself, deigning to hang with Jack and the troupe after hosting the TV show. To a man and a woman, they each embarrass themselves in attempting to curry his favor, and the look in Stiller’s eyes is priceless. It’s not that he’s mortified by these people. It’s that he remembers when he was one of them.

★ ★ ★
DON’T THINK TWICE

Written and directed by Mike Birbiglia. Starring Birbiglia, Keegan-Michael Key, Gillian Jacobs. At Kendall Square. 92 minutes. R (language, some drug use).