We know it’s wrong, just as he does.

But when teenage Adam lies to cute, cool New York lesbian Gillian, who thinks he’s trans, it’s funny. Because he then does his homework, mastering the jargon, the medical and psychological steps he’s supposed to be going through, working it to fit in with her crowd — at bars, parties, a “Women Only” S&M club — and to meet her expectations.

And when the horny teen visiting New York becomes a lovesick lad and dons a strap-on, because that’s what she expects? “Funny” flirts with “hilarious.”

Ariel Schrag, who made her bones writing for TV’s “The L Word,” was right making “Adam” a 2006 period piece. I’m not sure how much license we’d grant, even given her bonafides, in creating a situation that’s sure to be offensive to the gay community and having her “hero” (Nicholas Alexander of TV’s “Good Girls”) the-opposite-of-“woke” in the present day.

We need to laugh at Adam, and with him. Because, let’s face it, a “Women Only” S & M club with gay-and-trans women donning loaner leather and strap-ons for a simulated biker-bar oral sex contest is FUNNY.

But that’s only funny until Adam, and we, see the BIG error of our ways.

Adam and the movie about him turn on a dime, showing us the stakes in all the politics, all the marching, all the superficialities the straight or cis-gender attach to “gay” as a “lifestyle.”

People’s lives are at risk. Their right to live those lives as they see fit and their expectations for the future are at the heart of every head-scratching thing this fish-out-of-water kid observes in his full immersion in New York Gay — from “L Word” watching parties to “Trans Camp.”

These are activists living lives with consequences.

Schrag, director Rhys Ernst (of TV’s “Transparent”) and a delightful cast make “Adam” one of the great delights of the cinematic summer.

And you thought “Booksmart” was smart.

Adam is a suburban teen having no luck socializing with the opposite sex, but hellbent on not spending summer at “the lake house” with his parents, with Mom (Ana Gasteyer) realizing he’s “down in the dumpies.”

He’ll summer in New York, staying with big sister/coed Casey (Margaret Qualley). Maybe he’ll meet the new boyfriend she’s told the folks about, Mark.

Only there is no Mark. And Adam knows it. Casey, given a kid-in-a-candy-store flightiness by Qualley, the break-out star of “Once Upon a Time…in Hollywood,” is a young, beautiful lesbian loose in a city just loaded with young women just like her.

The kid brother is about to get an education, and how.

Casey is so over the moon about her new freedom that she’s taken up with a very feminine transgender person with the same name, “Boy Casey” (Maxton Miles Baeza). She broke up with cute truth-teller June (Chloë Levine, stealing scenes) to do that, something roommate Ethan (Leo Sheng) and even Adam can see was a bad move.

But there’s so much MORE to see that Adam can’t waste time on that. Go to the Washington Square march, hand out “Queers Against Gay Marriage” (don’t ask) fliers, borrow an ID to get into “the club.”

“It’s a dyke club,” June illuminates. “It’s full of dykes.”

If you think you’re having trouble with the “fluid” understanding of sexuality that’s become the norm today, imagine a virginal, sexually-insecure teen getting his mind around all this in 2006. Adam sticks his foot in it, defensive about wanting a “GIRLfriend” and not a boy one, tactlessly failing to grasp Casey’s thing for a guy who is “not a real guy, with a penis” and all.

Ethan, with whom he has an oddly intimate chemistry, becomes Adam’s guide and confessor.

Then Adam meets Gillian (Bobbi Salvör Menuez of “Landline”), an otherworldly redhead, at a party.

They click. But when she says “I’ve never dated a trans guy before,” he doesn’t correct her. And that’s where the movie goes, lie after lie, guilt and regret covered by “homework” and great efforts to fake his way through a relationship that races toward intimacy built on a bed of lies.

“I’m not actually ‘trans,'” and “I’m still in high school” are hard things to work into conversation after, you know, a certain point.

Schrag’s script, based on her book, is seasoned with some delicious one-liners, from the drunken bar-pickup who declares to Adam, “This is the year my poetry REALLY takes off” to the ever-enthusiastic Casey’s suggestion for what Adam take to the gay rights march.

“You should make a sign that says ‘I won’t get married until my sister can!'”

College coed Gillian is worried about majoring in Women’s Studies. “Hi, I’m gay and I’m majored in being gay!'”

And Adam, his eyes darting with apprehension at being found out, peppers his speech with the “hetero-normative” jargon that is part and parcel of the whole political/sexual/gender-identification lifestyle of it all.

Maybe it wouldn’t be this easy to “pass,” with every woman at the gay bar wanting to know “When did you, you know, transition?” But it’s hilarious to think an insecure guy would toss his last shred of masculinity just to gain the approval of the coed who prefers other coeds.

“Adam” makes you realize we’re a long way from “Chasing Amy.” Or maybe not.

Menuez gives Gillian a sort of knowing naivete and ahead-of-her-time enthusiasm, a youthful willingness to abandon what she thought she knew about who she’d be attracted to. Sheng and Levine bring great vulnerability to characters still figuring themselves out, sexually.

And Qualley sparkles as a willowy, pretty young thing aware of her allure to the gay women she meets, and unsure of what to do with that power other than to sample every candy in the shop.

“Pillow princess” might be the slang description that fits her Casey. Because heaven knows there are “gold star lesbians” all around her. It is 2006, after all.

See, Adam? You’re not the only one who does “homework.”

“Adam” is the sort of rom-com, coming-of-age tale that makes you want to.

MPAA Rating: unrated, with sexual situations, nudity, profanity

Cast: Nicholas Alexander, Bobbi Salvör Menuez, Margaret Qualley, Chloe Levine and Jari Jones

Credits: Directed by Rhys Ernst, script by Ariel Schrag, based on her book. A Wolfe release.

Running time: 1:35