A TikTok troll was arrested and charged Friday with fatally stabbing a 17-year-old boy, who inadvertently got between the online-provocateur and an angry mob that came to his home to confront him over claims he raped a young child, sources said. Andrew Tollinche, 22, allegedly stabbed high school student Jonathan Melo in the back Wednesday after the teen victim got caught up in the showdown at a Bronx apartment, which was sparked when Tollinche dared people on TikTok to face him down over the sex allegations, law enforcement sources said. During the encounter, Tollinche allegedly grabbed a large kitchen knife from his home and went outside to send the angry people fleeing, but allegedly wound up stabbing Melo amid the chaotic scene, sources said. TikTok troll Andrew Tollinche, 22, was arrested and charged with allegedly fatally stabbing 17-year-old Jonathan Melo on Friday.…