Too crazy and murderous to be exempt from having the finger pointed at her, Bellatrix's worst mistake is killing Sirius. Because how else do you get someone's blood up than by killing off the only family (ish) member that they've only just found. Harry's rage against Bellatrix is a deciding factor in his continuous hate campaign against her in the last few books. Her real weakness is her obsessive devotion to Voldemort, putting him above anything else, including her family. Bellatrix's evil nature borders on total insanity, causing her to act rashly and fervently, and in the Department of Mysteries, it is noted that the other Death Eaters present seem disturbed by Bellatrix's intensity. She is one scary lady.
I love Stephen King and music festivals; I eat my toast upside down; I daydream about getting married probably a bit too much; and I wish every day for a pet sausage dog puppy (who never materialises – sob).