I think this might have been popularized in the movie “Poltergeist II,” which in turn played on the late Heather O’Rourke’s earlier line in “Poltergeist” in which she exclaimed, “They’re heee-eeere!”
Shortly after “Poltergeist II,” the line would be used in a movie trailer for the Robert Carradine classic “Revenge of the Nerds II.” Carradine, whose back is to the camera, says "We’re [or “They’re] baaa-aaaack!”
Any earlier pop culture sightings?