Season 4, Episode 17 - The Toast Derivation
Aired February 24, 2011
With Leonard and Priya now dating, the gang are spending more time at Priya's apartment. Sheldon is uncomfortable with this change but is powerless to stop it. After realizing Leonard is the center of their social group, not him, Sheldon sets out to find a new group of friends who will have fun his way. Meanwhile, Penny tries to move on after seeing Leonard in his new relationship.