Ihbc means "I hate being copied", usually in reference to someone going out of their way to copy YOUR interests, what YOU'RE doing, or what YOU stand for as an individual. In short, "ihbc" is for individuals who hate being copied, or hate being copied by someone they dislike.
Dude 1: She's wearing that shirt you wore last week, she's suddenly into that one thing she hated before you, she cut her hair like you, she literally LOOKS LIKE YOU.