Sacha Baron Cohen looked like just another bro Sunday night, swilling a beer and mingling with college kids at a special screening at the Revere Hotel of his new movie, “The Brothers Grimsby.’’ It was the first time the movie — it’s part action flick, part gross-out comedy — had been screened for an audience outside LA, and the students from Emerson, Northeastern, BU, BC, and Harvard seemed to enjoy it. (“The Brothers Grimsby’’ opens March 11.) “I gotta say one thing: [expletive] Harvard! Who do they think they are?’’ Baron Cohen said by way of an introduction. “The bad news is we don’t have the movie. It didn’t arrive. We’re going to watch ‘Doctor Zhivago’ instead.’’ He was kidding, of course.