Two months after pleading guilty to a late-night, drunken, window-smashing rampage at the Ed Sullivan Theater, James Whittemore was back in Manhattan Criminal Court yesterday for allegedly punching a straphanger in the nose on a Harlem A-train platform.

“I lost it,” the 23-year-old admitted to The Post of throwing the first punch at an apparently deranged homeless man Tuesday at the 145th Street station.

“It’s the Irish in me. He wouldn’t leave us alone,” said Whittemore, who was with his girlfriend.

He was charged with misdemeanor assault, criminal mischief and harassment, according to court papers.

Whittemore has moved to Chicopee, Mass., since his notorious 2011 Stupid Human Trick — when he was found passed out drunk at David Letterman’s “Late Show” home.

“I cannot stand this place!” he said of New York City.