Rex Ryan’s mouth has gotten him in trouble again.

And he knows it.

“The thing that kind of gives this team a black eye when we’re looking at it is, I let my mouth get ahead of everything,” the first-year Buffalo Bills head coach said Monday on WGR 550 Sports Radio.

Ryan — who was fired by the Jets after six seasons and a 46-50 record — set lofty goals for his new franchise immediately after accepting the Bills job on Jan. 13. During his introductory press conference, he talked about building “a bully” in Buffalo and guaranteed Bills fans would see their team secure a playoff berth for the first time in 15 years. But in the months that followed, he and his players fell woefully short of those expectations.

The Bills, who have already been eliminated from playoff contention, are 7-8 heading into their season finale against his former team, the Jets (10-5).

“I think if I would have come in there and said, hey we’re going to compete and do all that stuff, maybe we wouldn’t have such a bad feeling about this team,” said Ryan, who signed a five-year, $27.5-million contract with the Bills. “This team doesn’t deserve that. This team has fought and played extremely hard. We’ve had a lot of things happen during this year, where we came up short. There’s no question about it. I think I could have handled it differently.”

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The bloom quickly fell off the proverbial rose in Buffalo, as fans and media began seeing cracks in the foundation of the AFC East powerhouse Ryan led them to believe he was building. And for the fifth straight year, Ryan will miss out on postseason play.

“We didn’t deserve to be in the playoffs because you’ve got to earn that and we didn’t earn it this year,” said Ryan, who was fired after the Jets finished 4-12 and failed to make the playoffs for a fourth straight season. “But we’re going to work extremely hard, I can promise you that, and give everything we have.”

The final hurdle of Ryan’s arduous season is Sunday’s game, which has playoff implications for his former club. If the Jets win, they’ll clinch a playoff berth for the first time since 2010 — when Ryan’s Mark Sanchez-led team made the AFC Championship Game for the second straight season.

This week, the Bills have nothing left to play for except pride. But Ryan believes that’s more than enough motivation.

“We want to enhance our season, and if we ruin their’s in the process, so be it,” he said. “But we want to win the game.”