Season 1, Episode 17 - The Tangerine Factor
Aired May 19, 2008
When Penny breaks up with her boyfriend after he posts intimate details about their relationship on his blog, Leonard tries to comfort her but inadvertently convinces her to get back with her ex-boyfriend. When it turns out her boyfriend has already moved on, Penny is angry at Leonard for his bad advice. Later, Leonard asks Penny out on a date and she says yes. Leonard and Penny each turn to Sheldon for romantic advice.
Season 4, Episode 15 - The Benefactor Factor
Aired February 10, 2011
The guys attend a university fundraiser where a wealthy donor takes an intimate interest in Leonard, forcing him to consider far he is willing to go for science.