5. Bonnie Wright as Ginny Weasley, Harry Potter and the Chamber of Secrets (2002)
Ginny is mostly inoffensive in the rest of the Potter films, but Chamber of Secrets finds her at her absolute worst. Having just started Hogwarts while nursing a huge, not-so-secret crush on Harry, she takes to writing in a diary—and the diary starts writing back.
This doesn't give her pause, even though unlike Harry she has spent her entire life in the wizarding world and should be aware enough to realize that something is off. By the time she finally starts to get alarmed, the diary's soul, a past incarnation of Voldemort, has already taken over her as a means to re-enter the world. The plot was cool, but the fact that Ginny fell for it always makes us shake our heads.