Season 9, Episode 3 - The Bachelor Party Corrosion
Aired October 5, 2015
When the guys head off to Mexico for the weekend to celebrate Leonard's marriage with a belated bachelor party, their science skills are put to the test when their van gets a flat tire. Meanwhile, the girls enjoy a low-key bachelorette party for Penny, which leads to her finally telling her family that she eloped with Leonard.
Season 9, Episode 21 - The Viewing Party Combustion
Aired April 21, 2016
Everyone must choose sides when a small argument between Leonard and Sheldon erupts into a heated fight during a group get-together.