It’s unclear at what point Lena Dunham was crowned the world’s Designated Expert on All Things (TM), but her latest chuckleheaded notion is to solve America’s gun violence by . . . editing the guns out of the ads for the new “Jason Bourne” movie.

“Editing” is too kind a word, since Dunham was responding to a “Girls” producer’s suggestion that subway ads for the upcoming Matt Damon film be vandalized en masse.

In an Instagram post, the producer, Tami Sagher, wrote, “Hey New Yorkers, what if we do some peeling and get rid of the guns in the Jason Bourne subway ads.” Dunham shared the item, adding, “Good idea . . . Let’s go!”

Let’s all beat up on subway ads? It’s literally graphic violence that Dunham is advocating. Where does this end? I picture armies of the night descending into the subways to denounce posters they don’t like. If they made a movie of this, it would have to be called “The (Social Justice) Warriors.” I didn’t say it would be a good movie.

If word gets around that it’s open season for images some people don’t like to be ripped out of subway ads, Dunham’s “Girls” posters are going to be minus a face pretty quickly. She has a lot of nonfans.

Dunham’s latest headline-generating act falls into the same category of many previous pronouncements: In all of them, Dunham’s attempts to court controversy look as strange and desperate for attention as playing pingpong topless. (Consider “Lena Dunham thinks dining hall sushi amounts to cultural appropriation,” “Lena Dunham, Hillary Clinton talk politics — and Lenny Kravitz’s penis” and “Diane Keaton thought Lena Dunham was a lesbian.”)

Dunham might not remember this, but back at the time of the 1999 Columbine slayings, America had itself a think about whether violent movies, video games or Marilyn Manson songs caused two kids to murder a dozen classmates and a teacher. After a few months, we came to our senses and decided that, no, the killers were just evil. (Except for the guy who won an Oscar claiming the murder idea had been implanted in the teens by thought waves coming off a Lockheed Martin plant).

Dunham’s attempts to court controversy look as strange and desperate for attention as playing pingpong topless

Everyone wishes they could edit reality, or at least edit the stuff we see on TV and at the movies. I wish I could install a filter on my TV that would digitally place a full-body parka over Lena Dunham during every cringe-inducing nude scene she’s filmed on “Girls.” But I can’t. (So instead I just stopped watching “Girls.”)

The handgun in the “Jason Bourne” poster isn’t even part of the national conversation on “assault rifles” (the term is vaguely defined), although sinister-looking rifles with scopes are certainly essential to the “Bourne” franchise.

But since, in an average year, more Americans are killed by “personal weapons” — i.e., hands and feet — than by all rifles combined, why don’t we have a national conversation on the former instead of the latter? Why don’t we edit them out of everything?

Sure, movies and TV shows would look strange if the actors had puffs of cotton candy where their hands and feet should be, but every foot and hand is a potential weapon.

And we can’t be too careful about what ideas we’re suggesting to America’s madmen.