Two quarreling city bus drivers locked horns and refused to move their massive rigs in a bizarre stand-off on a narrow two-way avenue in Brooklyn, a video released Friday shows. The B35 buses, each facing the opposite direction, stopped a few feet from each other on 13th Ave. near 39th St. in Borough Park about 6:45 p.m. Thursday, but both drivers refused to budge, sparking some gridlock in the area, the video shows. “Back it up! Back it up!” one of the MTA drivers screamed to the other. “How am I going to back up? Why can’t you back up?”...