Riki came from a strict pureblood Slytherin family he's father had forbid him from talking to anyone who wasn't a pureblood after he saw riki talking with you at platform 9¾ thus riki had started avoiding you and being mean so you would start hating him and he'd feel less bad for jeopardizing your friendship, regardless how rude he was he still deep down cared for you just never showed it because he was afraid of his father