As a general rule, you can’t pick your own nickname.

You can try. “Guys,” you say, “from now on, forget that I was ever called Eustace, and address me as The Punisher.” “Okay, Poop-stace,” everyone responds. Nicknames choose you.

There are only three real scenarios where you are able to select your own alias: You are still for some reason using AOL and trying to pick a screen name, you are a superhero or you have written something embarrassing that is about to see publication. Or you are about to leak a classified document.

For instance, Edward Snowden, the man behind the leaked 41 PowerPoint slides revealing the PRISM intelligence-gathering program, chose “Verax,” from the Latin for “truth teller.” Verax. As The Post reporter working with him noted, this was a loaded pseudonym. It had been taken twice before — once by a 19th-century writer who earned plaudits on the pages of newspapers, the other by a critic of Parliament who died in the Tower of London.

But the history of carefully selected aliases goes back further than that.

Publius was the collective authors of the Federalist Papers; Constance Dogood was Ben Franklin’s pseudonym for a time. Sometimes your alias outlives your identity. Mark Twain, the call of riverboat men on the Mississippi, was the chosen name of Samuel Clemens. And don’t forget Deep Throat.

As long as we’re speaking of “omniscience, automatic mass surveillance” like what Snowden described in his correspondence with “BRASSBANNER,” even George Orwell wasn’t the “1984” author’s real name. That was Eric Blair.

You can tell a lot about a person from his choice of alias.

Old screen names dog us down the decades. “” What were we thinking? “Javelin,” Mitt Romney, really?

Seldom do people pick names that are less idiotic than their original names. You never see the newspaper announcing that someone with a relatively dull, staid-sounding name has changed it to another, relatively dull, staid-sounding name. No, it’s always “John Doe has changed his name to Tyrannosaurus Rex, because he thought it sounded ‘cooler.'”

But the shell you choose to protect your identity says a lot about what you think you’re doing. Go with “Leaker” or “Verax”? “Anonymous” or “The Resurgent Arm of Justice”? Or is “The Resurgent Arm of Justice” protesting too much? Are you “Mr. Arachnid” or “Spiderman”? “The Incredible Hulk” or just “Angry Angry Bruce”? “Bat Man” or “Inspector Gadget”? “Verax” or “Truther”? “Deep Throat” or “Fellatrix”? It matters.

In general we aren’t very good at coming up with names. Is that “Google unique” or just impossible to spell? Superheroes have pseudonyms. Then again, so do supervillains.

The mask you choose shows how you see yourself and how you want us to see you. Snowden was a professional spy and unused to this publicity, but he knew the value of an alias.

A “Verax” by any other name might leak as many secrets, but it wouldn’t look as erudite on paper.

These days you hear Verax and you think it might be speaking for the trees, or cleaning rusty pans, because of what has happened to our educational system.

We met the mask at the same time as we spotted the man behind it, and now everyone is going to wage war over whether this was a case of Truthtelling or Dangerous Undermining of Our National Security (harder to convert into Latin). You cannot control what people see when they see the costume, but you can at least pick what’s on the nametag. Verax. Interesting choice.