One book that we have read is Chrysanthemum by Kevin Henkes.
Chrysanthemum has a long name and people make fun of her :(
While I was reading the story, each time someone made fun of Chrysanthemum, we passed a hear around and crumpled it a bit. Then, at the end of the story (which ended happily), we tried to smooth out the heart. We never got all of the wrinkles out. The heart will stay up in our classroom to remind us that once someone's heart is wrinkled (their feelings hurt), they never forget the hurt that you have caused them, because their heart is still a bit wrinkled.
You can hear the full story being read here: