Justin Sebik, 26, a bartender from Bayonne, N.J., was dismissed from the CBS reality show “Big Brother” late on Tuesday for holding a kitchen knife against the throat of a female contestant, the show’s executive producer confirmed Wednesday. Sebik had previously been warned about threatening behavior, producer Arnold Shapiro told The New York Times. But the producers held off giving Sebik the ax until several hours after the encounter with Louisiana waitress Krista Stegall, 28, who was reportedly not harmed. “Big Brother,” now in its second season, has been blasted by critics for being tasteless and by audiences for being dull. In the incident that sparked Sebik’s removal, a passionate kiss between Stegall and Sebik took a scary turn when Sebik started making threatening remarks. Sebik picked up a carpet sweeper and asked Stegall if she would be angered if “I cracked you over the head with this.” Not objecting, Stegall continued kissing him. Later finding the knife, Sebik asked, “Would you mind if I killed you?” The kissing continued, followed by the knife going toward her throat. Shapiro said that, although no one on the staff intervened at that moment, he and others were “on our feet” ready to step in.