BOSTON — A late-night trip to the movies turned into a bloodied mess when a Harvard researcher says he was swarmed by a pack of out-of-control teens inside AMC Boston Common.

Thiago Rentz, 35, had settled in for the horror flick Weapons on Sunday night. Instead, he says the real horror was the audience: a gang of noisy teens clapping, yelling, and disturbing everyone else in the theater.

“They were disturbing all of the people, clapping and screaming all the time,” Rentz told NBC10. He says he twice asked them to calm down.

When the credits rolled, Rentz says the gang formed a wall to block him from leaving, then unleashed a five-on-one pounding. He curled against the wall while fists rained down on his head.

“I didn’t fight back. I was scared,” Rentz said. “The target was obviously my head.”

The rambunctious rowdies bolted before police arrived. By the time officers showed up around 12:45 a.m., the Tremont Street theater was closed. EMTs treated Rentz for a bloody nose and a black eye.

Adding insult, Rentz says AMC staff were nowhere to be found. His friend eventually found a janitor, who dragged over a lone security guard. Rentz now wants surveillance footage reviewed so the teenage thugs can be identified. “They need to be punished,” he said.

AMC has not responded to requests for comment.

The attack is only the latest reminder that Boston’s “safe city” branding isn’t worth the popcorn bucket it’s printed on. Under Mayor Wu, even a late-night movie can turn into a brawl with out-of-control youths.