You can be invalidated by repeatedly being told through your life that your emotions are wrong, don't matter and/or are more volatile than the situation justifies. Validation is a key step in helping find a balance in BPD.
Lol. Happened just a few weeks ago, when I had to leave a group in my seminar at uni because the group wanted the guy they were with the week before and it was easy to get rid of me because I was the newbie. I understood where they came from, but it still hurt like a bitch and made me a little bit self-destructive.