A true New Yorker knows the right way to eat pizza – namely, with bare fingers.

As the horde of presidential candidates invaded the metropolis for primary election time they were given a lot of advice, some of it under the heading “Things That You Just Don't Do.”

A few years ago, Mayor Bill de Blasio and Donald Trump, two dyed-in-the-wool New Yorkers — “born and raised in the city” as native New Yorkers say — were gleefully attacked when they were spotted in public using knives and forks to eat their pizza. The cocky billionaire was targeted because he had invited Sarah Palin, the tea party movement's Joan of Arc, to lunch in a fast-food pizzeria. That's all it took to cause a firestorm on the boulevard: When it comes to lifestyle, those abrasive New Yorkers can be terribly sensitive.

Now Hillary Clinton and Bernie Sanders have failed their road tests in the New York subway: one of them couldn't get through the turnstile with her Metrocard and the other thought the key to “Open Sesame” was to insert subway tokens (which haven't been used for years). It was doubly embarrassing when Donald Trump — the self-anointed patron saint of 9/11 victims — referred to 9/11 as 7-Eleven, the name of a popular convenience store chain in the U.S.

That faux pas might have cost “The Donald” a couple of votes but it was nothing compared to the ridicule he had to endure.