The guys are invited to Penny's Halloween party, first turning it down as they 'don't dance' but changing their mind when costumes are mentioned. Once at the party only Wolowitz and Leonard attempt to socialize; with mixed success. Penny's ex-boyfriend Kurt shows up and humiliates Leonard, causing him to leave. Penny goes to check on him and apologizes. Both drunk and upset she kisses Leonard, which he refutes with the obvious reasons as to why she's doing it. Penny says he's sweet and wonders why more men can't be like him, with Leonard replying, "Because the human race wouldn`t survive". Penny goes to leave and kisses him once more in the doorway. Meanwhile, Wolowitz can not find Koothrappali, who ends up going home and has sex with a girl he had met at the party, who found him to be a 'good listener' (as Koothrappali is so shy he can not speak to attractive women). Penny hosts a Halloween party, putting Leonard, Sheldon, Wolowitz, and Koothrappali through a new test of their social skills.