Among the many contentious ideas explored during Bad Jews, Joshua Harmon’s delicious pressure cooker of a show now playing at the Geffen, is how a religious or cultural identity can become the sole bedrock upon which some people base their identity. Having lobbed this hand grenade onstage, the play proceeds to ask, cheekily at first and then with real concern, whether this degree of self-assuredness is a good thing. The method — a knock ‘em down, drag ‘em out free-for-all among three young representations of contemporary Judaism — could hardly be more entertaining, but it’s not for the faint of heart.

Directed by Matt Shakman, the Geffen production starts off at a light jog and ends running flat out toward the finish line. The action takes place in the Upper West Side studio apartment of Jonah (Raviv Ullman), a taciturn host whose cousin Daphna (Molly Ephraim), a Vassar undergraduate who knows and uses the correct plural of “syllabus,” is bedding down at his place following the funeral of their grandfather earlier that day. They’re soon joined by Liam (Ari Brand), Jonah’s older brother, and his girlfriend Melody (Lili Fuller), who’ve just flown in from Aspen, missing the service by hours due to a smartphone mishap.

Daphna, as Liam enjoys venting to his brother approximately 30 seconds after his arrival, is a “Super Jew” who until recently was known as Diana: After acquiring an Israeli-soldier boyfriend and enrolling in a prerabbinical course, she’s decided to move to Israel following graduation. Liam, a Ph.D. candidate in Japanese cultural studies, fails to keep Passover and only likes to trot out his Jewish identity when he can use it to bash all things Jewish, Daphna later accuses him. They both, we learn through independent conversations, have their eye on their grandfather’s chai necklace, a Jewish symbol and dear family heirloom that survived his time in the concentration camps. Daphna thinks her devout Jewishness gives her the rightful claim. Liam has other plans for it.

At a performance this past week, the promising cast hadn’t quite ironed out all the slack in their performancs. The first 20 minutes doesn’t have the snap it could: Ephraim and Ullman are still figuring out how to tease the maximum comedic value from Daphna’s runaway-train monologue, and her character’s obnoxious personal habits feel at times too consciously cultivated. But once the cast is complete, things get cracking. Brand’s twitchy, tightly wound Liam seethes at every casual provocation, working himself up into venemous tirades. Ephraim’s effortless dismantlement of poor Melody is a sight to behold, setting conversational traps with a lazy, disinterested tone that belies the instincts of a scorpion. Fuller is the show’s comedic secret weapon, delivering one of the play’s funniest scenes with a rendition of “Summertime,” complete with scrupulously reproduced dialect. Ullman makes a superb and dignified straight man.

Behind the fireworks, however, lie real and painful questions, which can resonate with audiences of all creeds: What responsibility do the survivors of tragedy and their descendents bear to the past? If identity is just a construct, does that matter? Should it? Are people really just people?

Bad Jews doesn’t offer authoritative answers to those questions, but it does blast open the door for uncomfortable conversations on the car ride home from the theater.

GO! Geffen Playhouse,10886 Le Conte Ave., Westwood;  through July 19. (310) 208-5454, www.geffenplayhouse.com.

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