An already overrun selfie spot in Brooklyn that’s battered by thousands of tourists a day is about to become even more of a chaotic mess with the World Cup this summer, frantic locals told The Post. The world-class view of the Manhattan Bridge in trendy DUMBO has drawn busload after busload of visitors to Washington Street daily since the spot went viral as a picture-perfect backdrop a few years ago. But along with the massive crowds have come hordes of price-gouging aggressive street vendors, smelly trash and rats — and the mayhem is only expected to worsen thanks to the expected 1.2 million FIFA fans set to flood the city, residents said. A spot in Downtown Brooklyn provides the perfect selfie backdop for photos with the iconic Manhattan Bridge — and headaches for locals. Michael Nagle “It will take a catastrophe before anything changes,” lamented local Tara Quinn.…