BOSTON — The rule is dumb, yet somehow Michael Pineda was more foolish than the rule.

There’s an unwritten understanding among combatants that pitchers can take a sticky substance to the mound on a cold night to better grasp the slick baseball, as much to protect the hitters from unguided flying objects as anything.

That everyone is in on the wink-wink understanding means Major League Baseball should just change the rule so a pitcher can use a tacky substance legally once the weather drops to a certain temperature — and it was 50 degrees at game time with strong winds Wednesday.

But as long as this remains a rule, all that anyone asks within the game is don’t be blatant about the “cheating.” Think of it as the 10 mph courtesy above the speed limit drivers are generally allowed before being busted for speeding. You can go 62 in a 55 zone, but don’t go 82.

Heck, before a pitch was thrown Wednesday night Boston manager John Farrell had said: “I would expect if it’s used, it’s more discreet than the last time.”

He was talking pine tar and Pineda, and he was answering a question about this because the last time the righty had faced the Red Sox just 13 days earlier a tempest had been caused when what looked like a large dollop of pine tar was shown on his pitching hand. Pineda claimed it was dirt.

Whatever, it should have been lesson learned from the furor it caused. Hey, Mike, if you are going to cheat be discreet. You dodged this once, please, please don’t force your opponent’s hand to act — particularly the same opponent who just happens to be your most bitter rival.

Instead, after his worst inning of the season — a 30-pitch, two-run first in which he threw just four of his trademark sliders — Pineda emerged for the second with a discoloration on the right side of his neck that had all the subtlety of Mike Tyson’s face tattoo. It looked as if the worst makeup artist in the world was drunk and had at him. It was certainly distinct enough to be caught by three networks — YES, NESN and ESPN — televising the game.

So with a 1-2 count on Grady Sizemore, Farrell could not avoid the obvious any longer. He asked home-plate umpire Gerry Davis to check Pineda. The crew chief eventually touched his finger to Pineda’s neck, rubbed his fingers together to feel the tackiness, immediately ejected Pineda and mouthed, “It’s pine tar.”

With that, Pineda went from a Comeback Player of the Year front-runner to Most Likely to Deceive — Poorly. He hurt his rep and his team, forcing the Yankees to cover 6 ¹/₃ bullpen innings in a 5-1 loss.

Pineda would explain afterward he made the decision because he couldn’t grip the ball in the first. He insisted it was about hitter safety, not to gain an unfair edge. But Yankees officials said he had been warned many times since the first incident what the implications of doing this again would be. They were clearly befuddled by what Pineda did, annoyed at what he did.

But general manager Brian Cashman also acknowledged this as a systemic breakdown by the whole organization and “an embarrassment” that Pineda did not absorb the message and “would take the field in the second inning with that on his neck.”

Cashman said Farrell did exactly what he would hope manager Joe Girardi would when misbehavior is so overt. It would have been negligent at that point for Farrell to accept this as acceptable brinksmanship. Not with this much attention on the matter.

Pineda either panicked into a headstrong mistake or didn’t calculate the ramifications well or didn’t care. Whatever the result, he retreated to the clubhouse and no mechanism existed to stop him from turning his neck into a pine tar Rorschach test.

“He made an error in judgment,” Girardi said.

Pineda will be suspended; precedent is eight to 10 games. If it is eight and served immediately — because of a Monday off day — the Yankees might not even need to use an extra starter. But the ramifications carry beyond this short period.

Pineda apologized to his teammates, but until proven otherwise there will be internal questions about his savvy and ability to react well under stress. Girardi and Cashman both said they think the righty can pitch well without the aid of pine tar and that this incident will not leave a psychic scar — that he has overcome too much battling back from shoulder surgery to be unnerved and undermined by this.

But we will see. This is now on his permanent record, the GIF that keeps giving will be that blob on his neck, the word pine tar associated with his name.

Shakespeare gave us “The better part of valor is discretion.” Michael Pineda needs to learn that applies to the better part of baseball cheating, as well.