Season 1, Episode 3 - The Fuzzy Boots Corollary
Aired October 8, 2007
Leonard's hopes of a relationship with Penny are dashed when he sees her kiss another guy, so he decides to ask his colleague Leslie Winkle out. When Leslie is uninterested in going out with Leonard, he feels dejected and thinks about getting a cat. In an attempt to buoy Leonard's spirits, and stop him getting a cat, Sheldon encourages Leonard to ask Penny out on a date.
Season 3, Episode 5 - The Creepy Candy Coating Corollary
Aired October 19, 2009
When Raj and Sheldon enter a Mystic Warlords of Ka'a tournament at Stuart's comic book store, Sheldon gets the opportunity to settle an old score with his nemesis, Star Trek: The Next Generation's Wil Wheaton. Meanwhile, Leonard regrets a pact he once made with Wolowitz when he must ask Penny to set him up with one of her friends.