For me its when my family flew in for my graduation and they also decided to meet my sister's in-laws. After graduation we were supposed to go to a restaurant. The ceremony was supposed to last two hours but stretched to four and we were about to miss our reservation. My sister pressured me to leave even tho I didnt have a chance to take pictures with friends and such. I have mostly moved on but honestly a part of me still hates her for it.
I feel ya. Trying to forgive is always the best with family cuz you only get one. Good luck on working to have a different/better relationship with them as an adult.