It seems to be mainly if she's annoyed, if she can't have her own way. She'll bang her head on the floor or chair or whatever but then she'll be more upset because it hurts and she knows it hurts but will still do it again. She also bangs her head on the sofa just when she'd sitting there, no obvious reason but I don't mind that so much because it's soft.
Any one else's kid ever do this?
What's the best way to react? At the moment I either ignore her completely or just say "Ouch, yes I should think that did hurt", but I don't make a big fuss.