Is "a guy's girlfriend" from Obsession? (Oh, I see the spoiler.) Also sorta applies to It Follows, though the stalker wasn't anyone in particular; in fact, it could be "anyone".
How about "an adorable little girl who looks at you funny"? Samara from The Ring (RIP Daveigh), MEGAN, Arya Stark from Game of Thrones if you're one of the dozens of people she killed... there have got to be more. Wednesday Addams was kind of a horror icon, or tried to be. It just seems there are a lot of creepy little kids in horror.