ITBitch isn't winding you up? He's definitely done it?
She's going to go nuclear! Hopefully she will think and realise it's been done today, rather than that you did it last night.
Also, as entertaining as I'm finding this, I'd be prepared for her to make a formal complaint to HR about it.
Unfortunately, I think that what your office needs is a formal, published 'fridge usage policy'. This is the kind of thing that drives our HR manager nuts- she tries not to have lots of silly policies for things like the 'correct use of the fridge and cloakroom', because she thinks we're adults and should know how to behave, but some idiot invariably messes things up so that she has to write a policy, and we all have read them. She always says we've brought it on ourselves 