A visitor to the Met who thought a painting was hanging crookedly decided to fix it himself Friday evening — then used a bottle of wine he’d smuggled in under his jacket to clock a security guard, sources said.

The Metropolitan Museum of Art guard, Mark Burns, 46, was struck after telling the outraged “critic’’ to keep his hands off the art.

Burns was taken to Weill-Cornell Hospital with a head laceration.

His attacker fled and cops were checking video to try to identify him.