“A young black man is suing both the NYPD and Barneys for wondering how in the world he could afford a $300 product, then harassing and arresting him. Trayon Christian, who was 18 at the time, bought a Ferragamo belt he’d been coveting from the department store after receiving a paycheck from his work-study job. “I wanted to go to Fifth Avenue, I knew exactly what I wanted,“ he told the Daily News. But on his way out, he was handcuffed. Two undercover detectives accused Christian of using a forged debit car