You could start by just noticing. Notice the neutral comment, notice where your mind goes, knowing it may or may not be negative.

I'm the same way, btw, and I have a difficult past too.

Another thing you could do is journal. Don't spend too much time ruminating over it, but there Are productive ways to journal. I do a T chart sometimes. On one side, goes all my negative thoughts. On the other side I counter those thoughts with more positive kind words.