Horrifying video footage shows a tracksuited man casually heading into a small Big Apple boutique — then leaping across the register to slash the lone store assistant across the face. The attacker — wearing a distinctive black Adidas tracksuit with purple and orange bands on the arms — was caught on surveillance footage shared by the NYPD as he casually strolled down Audubon Avenue in Washington Heights just after 3:40 p.m. on Friday. He paused to put his face up to the window of Steph’s Designs, walking inside to casually talk to the lone staffer, Desteny Cabrera, who did not know him, the NYPD said. After initially having his hands in his pockets, within seconds of chatting he suddenly leaped across the counter — slashing the 22-year-old stranger across the face, the footage first shared by the store shows. The knifeman fled from the store, tripping as he ran outside before racing across the street. Footage posted by the store shows Cabrera standing up in shock — with blood pouring from her face into her hand.