Kaley Cuoco Recalls "Terrifying" Encounter With The Big Bang Theory Fan ✖ Big Bang Theory star Kaley Cuoco is no stranger to encounters with fans. After playing Penny on the popular sitcom for twelve seasons, Cuoco's built up quite a fan base who recognizes her even when she's travelling. And while most fan encounters are pleasant, some aren't. That includes one "terrifying" encounter Cuoco had while on a plane that involved a flight attendant and Sheldon Cooper's (Jim Parsons) infamous triple-knock. Speaking with USA Today, Cuoco recounted an experience in which she didn't quite get the fan's intended joke making for a frightening and perhaps confusing situation.