Not to derail the thread, but here is one example from my life. My older sister is somewhat of a golden child, at least in her own mind, and she is extremely competitive with me. I could not ever possibly measure up, in her mind (not in mine - while I think her life is fantastic, I don't feel the need to make comparisons - I am happy with my life), and it frustrates her that I don't engage in the competition.
My toddler was acting up at a family holiday meal, and I told DD that if she did not do X (I think it was stop going under the table and eat some bites of her food), Y would happen (I think it was she would not get the fabulous dessert my mom made). My child did not do X, so Y happened. DD began screaming and I took her away from the table until she was calm and brought her back. She did not get dessert until after she ate the bites of her food. Personally, I think I handled it well. DD has improved since then. She was maybe 3 at the time.
My sister, the next day, sent me an email chastising me for how I handled my child (she has four kids) and that my leaving the table with my misbehaving toddler ruined the meal. I should not have denied her dessert on a holiday (never mind she did get dessert, I just made sure she actually had some real food first). My response was that I was saddened to learn that she disapproved of my parenting (which, for the record, is what she does also and her children "ruined" many many meals over the years in the same way), but that I had thought about how to handle my DD, was doing the best I could, believe I handled the situation well, and that if she was uncomfortable with how I am parenting then maybe we should not spend time together if it is upsetting to her.
I got an apology. My sister saw where I was coming from and that her disapproval of me might affect her, but wouldn't affect me. Now, my family isn't perfect, but especially as we get older we are really working hard to not be petty and to treat each other with respect and love.