Tell me the worst thing you've ever done to a friend?

For example, birthdays, important exams, and minor disasters around me will always receive greetings and comfort at the first time, but I always forget when it is my turn. I am always annoyed when I have something to do. No matter when or where, there is always a warm face waiting for me. In retrospect, I'm sorry that I don't deserve such a good friend. These are all terrible things I did to her.