Warning: The contents of this video may be disturbing to some viewers. By now, you've probably heard about or seen Sam Pepper's "Killing Best Friend Prank" video, where the blue-haired YouTuber pranks Vine user Sam Golbach, whose best friend Colby Brock is in on the joke. By the end of the video, Golbach is emotionally distraught after believing he witnessed a masked stranger execute Brock before his eyes.