Mayor de Blasio, a self-professed Boston Red Sox fan, must still be upset about the Mets’ 1986 World Series win over his old hometown team — as he chose to skip their big pep rally at Queens Borough Hall on Monday.

“The Mayor’s schedule didn’t allow for today’s rally,” a spokesman said. “He’ll be rooting for the Mets tomorrow while they’re in Kansas City and can’t wait for them to come back to Queens.”

Some 1,500 fans and officials showed up for the event at 3 p.m., most decked out in orange and blue.

“I think that we had such a great crowd here today,” explained borough president Melinda Katz, who hosted the rally and sent out invites to officials on Friday.

“Folks showed a lot of New York pride,” she said.

While many city officials and public figures were at the event — including Council Speaker Melissa Mark-Viverito, former players John Franco and Eduardo Alfonso and even Mr. Met himself — de Blasio chose to play hooky, sparking outrage from several in attendance.

“It’s a shame,” said Ima Gattas, an FDNY EMS worker from Kew Gardens. “The New York Mets are New York. It’s the team of all New Yorkers and the mayor represents all of us. That’s why it’s upsetting. Just show up few minutes and say, ‘I’m rooting for you guys.’”

“He should have come to this,” said Felix Aponte, a 70-year-old retired NYPD cop and sanitation worker from East New York. “Why is he not here? He’s not representing the city the way he’s supposed to. When you become a mayor you become part of the city, and you’re supposed to be here with the city, not traveling, not sitting in your office. The last time the Mets were in the World Series was 15 years ago, and he didn’t have the courtesy to come and share in our happiness? That’s not right.”

Michael Fandal, a 66-year-old retired NYPD cop from the Upper East Side, agrees — but would rather have the mayor stay at home than be forced to see him act like a fair-weather fan.

“I”m pleased that I don’t need to be anywhere near him,” he said. “I don’t want to breathe the same air as him. He doesn’t care about baseball. He’s devoid of any sense of humor, and baseball and him don’t go together. Baseball is about the great values of the United States and I think he’s remiss. It’s not a surprise to me that he’s not showing up.”

But despite the outrage, Katz jumped to de Blasio’s defense when asked if she was disappointed that he couldn’t make it to the rally.

“I’m sure he’s rooting for the Mets somewhere,” she said.