The ex-con accused of slitting a French tourist’s throat in a random attack in Harlem is a neighborhood “neck slasher” who’s ducked justice at least twice — infuriating one of his alleged victims, The Post has learned. Khalief Young — who is charged in Friday’s horrific attack on Gabriel Bascou — was busted in June for a Harlem deli slashing, and in October for allegedly pummeling a woman inside his apartment building, according to police sources and court records obtained by The Post.