NEW YORK — Actor Anthony Rapp’s lawyer asked a Manhattan jury Thursday not to believe Kevin Spacey’s Oscar-worthy performance on the witness stand — but to find him liable for preying on Rapp a teenage boy 36 years ago. “When you’re rehearsed and a world-class actor and you’re following the scripts and following the testimony of someone else, you can take that stand and be perfectly polished,” Rapp’s attorney Richard Steigman said in Manhattan Federal Court. The “Rent” star’s $40 million lawsuit accuses Spacey of coming on to him as he was starting out on Broadway when he was 14 years old. Rap…