This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / 2 Broke Girls
Max's very visible pain when she finds out Johnny has a girlfriend.
Max's good bye to Chestnut when they have to send him to a shelter for the winter.
Max telling Caroline that she uses store-bought cake mix because no one ever taught her how to bake, or how to do anything, and asks Caroline if she really thinks that Max should get her mother a better birthday card.
When Max is electrocuted and Caroline thinks she might die, she begs Max not to die, trying not to cry, because she's her best friend.
In season 5, Caroline's Ex Andy returns, only to announce he's marrying some one else. Caroline really had a hard time accepting it.