A hate-fueled attacker allegedly pummeled a stranger who simply glanced at her in an unprovoked attack onboard a Manhattan train over the weekend, cops and sources said. Genesis Gittens — who just turned 20 on Monday — was yelling on a southbound L train at the 1st Avenue and East 14th Street station around 2:10 a.m. Sunday when a 28-year-old man sitting in front of her turned to look, authorities and law enforcement sources said. Gittens then flew into a rage, repeatedly punching the straphanger in the face as she sneered, “White boy” and “cracker,” according to a criminal complaint....