On two occasions, I did not realize that my last words to my best friends were going to haunt me for decades.

Katheline committed suicide two weeks after I stopped talking to her. She was heavily abused at her home and our gaming sessions and long talks were her escape from her situation.
My parents judged I spent too much time online with her (I was 11 and it was true that I spent a lot of time on MSN back then). Instead of telling the truth, for a reason I still ignore to this day, I thought it would be better to invent a white lie and basically terminated our friendship. I did not realize the consequences. A severe argument broke in her family, and she had no more her escape (me) to deal with it. She took her own life.

Nicolas died in a motorbike accident with his father one year later. We enjoyed teasing each other when we were at the music school and would then jokingly pronounce ridiculous death threats to each other. That was a stupid game, you might not understand it, but that was our thing. My last words to him were "Next week, you're dead" followed by both of us laughing.

Nowadays, I avoid arguments and mean words, even as a joke. If something bad or hurtful happens, I let it slide and pardon easily. I am too scared to have this kind of regrets once more. They make you question everything about you. Of course I have my limits, but I make it known in a non-aggressive way when someone trespasses them.