Barty is a year older than you, it's his second year at Hogwarts and your first. From the moment he saw you he was interested in you, he watched your every step, but you never realized this, until an ordinary potions class.

In this class, he was watching you and wasn't being discreet, so you look in his direction. His body reacts and he stares at you, and you just say, "you're creepy."; and well, it's since that day that he started to hate you.