The Amityville Horror. I read lots of scary/horror books (especially true stories) and I don't know why that one scares me the most. I can't keep it in the house (remember Friends Joey keeping The Shining in the freezer? I know how he feels.)
I don't care if it's a hoax, it's darn scary.
Reminds me of two things:
In M.R. James' short story "The Mezzotint" (the first real ghost story I ever read and which terrified me for days on end) the protagonist takes the etching he's purchased and which is revealing to him a horrifying story he'd rather not know and, with picture between thumb and forefinger, he walks it across the hallway to his "other set of rooms kept as an office" and puts the picture into a drawer in a desk, face down, placing (I think) a book on top of it. Then he locks the drawer, shoves furniture in front of it and then locks the door to those rooms as well. In later years I was able to appreciate the humor in that scene (and James makes clear that he's having a bit of fun at his character's expense) but in the seventh grade, all I remembered was the Shape as it creeps across the lawn.
What makes me laugh about Joey and the fridge, is that, I had purchased some H.P. Lovecraft for a friend's birthday. I had never read Lovecraft before and so was tempted. I remember something about a hill that ate hunters climbing up to it and a few happy others like that. I took all three books, but them by my front door, face down, and then piled on two copies of the encyclopedia plus a bible. I decided I was insane until, a few years later at a Horror Convention, I met a woman who had done the same thing and with the same book.
I don't know if I felt less crazy, but I was glad to know other people did that.