This isn't in the same league as some of the fucked up shit going down in this thread, but it does a good job of illustrating what a crappy relationship I had with my parents.
When I was growing up, my sister was the star of the house. They had her pegged as some kind of genius, while I was always considered the dullard and dumbo who would be lucky to graduate highschool. She went to a very expensive private school, I went to the local highschool. There were pictures of her all over the house, and I was the invisible boy.
In any case, I gradually grew away from them and left for university...the same university as my sister. We soon discovered that I was not in fact the dullard. I was blossoming and she was struggling. She was getting shitty grades and I was all of a sudden getting A and A+ grades. Time goes by and she got miserable marks on her SAT, failed to get into Law School, and ended up leaving after a second-class arts degree with a B average. I got a scholarship to Oxford to do a post-graduate research degree.
Despite all this, when I got the letter of acceptance and the offer,my parents literally thought that I was too dumb to understand that what I had received was, in fact, a rejection letter. They thought I had mistaken getting rejected for getting accepted! Even after all the awesome scholastic achievements I had, they still thought I was a fucking moron.I don't think I'll ever forget the conversation I had with them at the time: "Arrrreeee you suuuuuuuurrreeeeee they are accepting you???"
I'm now the only one in my entire family tree with a PhD. So fuck them.