236 The Big Bang Theory The Nerdvana Annihilation 01 14 2008-04-28 Comedy / Romance Jim Parsons - Sheldon Cooper / Johnny Galecki - Leonard Hofstadter / Kaley Cuoco - Penny / Kunal Nayyar - Rajesh Koothrappali / Simon Helberg - Howard Wolowitz / Melissa Rauch - Bernadette Rostenkowski / Mayim Bialik - Amy Farrah Fowler / Laura Spencer - Emily Sweeney / Sara Gilbert - Leslie Winkle / Kevin Sussman - Stuart Bloom / John Ross Bowie - Barry Kripke / Carol Ann Susi - Debbie Wolowitz When the guys buy a time machine prop from a classic 1960 movie, Penny lashes out at Leonard and he decides it's time to give up his habit, much to his friends' protestation.