Let's see... when I was 5 my mom made me watch Jaws with her. I thought Jaws was the character from the cartoon show James Bond Jr. Needless to say, when the shark first appeared, I jumped out of her lap, yelled my first swear phrase (Holy sugar... replace the second word with another s-word lol), and became paranoid of going into lakes and larger bodies of water lol.
Growing up, she also made me watch timeless classics such as Halloween, Hellraiser, Friday the 13th, Texas Chainsaw Massacre, A Nightmare on Elm Street, and countless other horror films (including probably all of the sequels). After seeing all of them at a young age, I became completely desensitized to any new horror films that have been released and typically laugh at them while my girlfriend and friends close their eyes.
My favorite movie out of those: Jaws