There’s a new phrase echoing through school hallways — and it’s driving teachers up a wall. “Six-seven! Six-seven!” is not a math problem. It’s the latest Gen Alpha obsession — and educators across the US (and some in Australia) say it’s gotten so out of hand, they’ve had to ban it from classrooms altogether. The mysterious slang term comes from the viral song “Doot Doot (6 7)” by rapper Skrilla, which features the endlessly repeated lyric “six-seven.” The phrase — which can mean nothing,