Season 1, Episode 9 - The Cooper-Hofstadter Polarization
Aired March 17, 2008
When Sheldon and Leonard are asked to present their work at a physics conference, Sheldon unilaterally decides not to. Leonard and Sheldon feud when Leonard decides to present their work alone in spite of Sheldon's objections. Penny's attempts at reconciling the pair only make matters worse.
Season 2, Episode 7 - The Panty Pinata Polarization
Aired November 10, 2008
When Penny inadvertently breaks one of Sheldon's rules by touching his food, she finds herself the victim of his "three strikes and you're out" policy. After being banished from the apartment, Penny seeks revenge on Sheldon, leading to all-out war between them.
Season 7, Episode 16 - The Table Polarization
Aired February 27, 2014
When Leonard buys a new dining room table for the apartment, Sheldon starts to reconsider the changes in his own life. Meanwhile, Bernadette doesn't know how to react when Howard is offered the chance to go into space again.
Season 11, Episode 21 - The Comet Polarization
Aired April 19, 2018
When author Neil Gaiman gives Stuart's comic book store a popularity boost, Sheldon is uncomfortable with the changes at the Comic Center. Meanwhile, Raj takes credit for an astronomical discovery made by Penny, putting their friendship at risk.