Good romantic comedies remain Hollywood’s most elusive unicorns, and maybe there’s a reason for that. Maybe it’s a thesis put forth in “Playing It Cool,” a mediocre, gimmicky 2015 romantic comedy that featured a star-studded supporting cast, some cute characters, witty banter and adorable leads.

Maybe screenwriters are the last people to know a damned thing about “true love.”

Our hero and narrator (Chris Evans) admits as much. For all the “You can’t put love on paper” complaints of his writer pals, all the “Rom coms aren’t true. They’re what we wish were true,” advise from his agent (Anthony Mackie), you can’t be en emotionally stunted heel with a dead spot inside and write great romance.

I’m not necessarily buying that, but “Cool,” the first and so-far only feature of its director and one of two credits by its Chris Evans-connected writers (their sad-romance “Before We Go” came out at about the same time) makes its case and as we dissect what went wrong, it seems to make its point.

Romantic comedies demand that we’re shown a couple we want to see together, people we root for. And are there two more likable leads than Evans and Michelle Monaghan? Did you HEAR Evans sing in “The Losers?” Have you seen ANY Monaghan movie? Ever?

The genre has its conventions, which stretch to Shakespeare — obstacles, romantic competition, weddings and the “Act Three running through the airport” scene accompanied by bystanders giving the lovers “the slow clap” when they finally embrace.

OK, the airport bit doesn’t date from Shakespeare, but all the rest? Those are the rules our narrator must follow, as related by is writer-pal Scott (Topher Grace). So why can’t he get them into hi screenplay, “Splinter,” about two people with multiple personality disorder who fall in love?

“They have Ashley Tisdale from ‘High School Musical’ and Matthew Morrison from ‘Glee!’ It’s gonna be HUGE,” his agent says. “I can see the poster, now.”

But our hero just isn’t feeling it, and as never felt it. Even projecting himself into the romantic tales of the grandpa who raised him (an animated World War II romance and combat sequence) and his circle of writer-friends (Grace, Aubrey Plaza, Luke Wilson, Martin Starr) doesn’t help.

Until he starts seeing this woman he met at a charity dinner (Monaghan), who never told him her name but did let him see she had a boyfriend (Ioan Gruffudd) in these projection fantasies. Sometimes he’s the hero of a Korean soap opera they’re talking about, sometimes he’s his pal Mallory (Plaza), in a wig and dress, getting groped by her handsy date, but always he shares this moment, in his mind, with the stranger played by Monaghan.

That’s chief among the gimmicks of this gimmicky rom-com. The narrator sees himself in his “writer” guise — cynical, smoking and drinking in a black suit and Homberg hat. He wanders, black-and-white, through a world of lovers living out their romances in color all over Venice Beach.

The irony of ironies here is that this quick and cold and stunningly cluttered comedy is Exhibit A in ways a rom-com can’t work. The film has so much going on that we don’t connect the lovers and never have a chance to root for them.

Their “meet cute” in the first act is promising, with her overhearing him diss the other women at their charity dinner.

“If I have to hear one more ‘4’ talk about her vegan pet, my sperm are going to start eating each other.”

After that? Bupkis. Pretty much.

Evans rounded up a legion of former and future co-stars (Mackie, Gruffudd) and actors like Patrick Warburton and Philip Baker Hall (as is grandfather) show up for a couple of scenes, make an impression and exit.

There are several scenes with his “family” of writers — at a shooting range, on the beach, in a bowling alley. The banter is overfamiliar men saying what women are like, and vice versa, save for riffs about writers with sexually suggestive names — “Shakespeare, Longfellow. ee cummings. Balzac. Atwood. Koontz. Longfellow.”

A cute analogy or three — “Love is like a leak in a boat. It starts slowly, and if you don’t stop it, you drown.” “You know what this suit’s made out of? Boyfriend material!”

But the rest is just cliches that aren’t really turned on their heads, tropes that play like the high five instead of a kiss at “the right moment,” which means he gets to “hear it echo to the end of eternity.”

Because our hero, like our screenwriters, can’t manage sweet. But writing a rom-com that is “Not funny, not romantic, love how it really is” isn’t quite within their reach, either.

MPAA Rating: R for language and sexual content

Cast: Chris Evans, Michelle Monaghan, Anthony Mackie, Topher Grace, Aubrey Plaza, Luke Wilson, Ioan Gruffudd, Patrick Warburton, Philip Baker Ball

Credits:Directed by Justin Reardon, script by Chris Shafer and Paul Vicknair. A  Vertical/Voltage release.

Running time: 1:34