Friends/Tear Jerker

While Friends is usually a very light hearted and optimistic show, it's had a few notable examples.
 * After Rachel finds out about Ross's feelings for her in "The One Where Rachel Finds Out" and realizes she feels the same way, she decides to meet him at the airport as he comes back from his week long arecholgical dig in China, only to find Ross getting off the plane with his new girfriend Julie.
 * Monica and Richard's break-up in "The One With Barry And Mindy's Wedding".,
 * Rachel finding out about Ross sleeping with Chloe the copy girl in "The One On The Morning After" and their massive fight and break-up afterwords is easily the most devastating and gut-wrenching moment in the entire series.
 * The series finale has several emotional moments, but their are a couple that really stand out. While we all know Rachel , her initial rejection of Ross at the airport and his breakdown after it are incredibly heartbreaking.
 * In the final scene of the series when the friends leave Monica's apartment for the last time, also counts as a Crowning Moment of Heartwarming.