Following on from the other thread, and apart from seriously evil stuff that my last nanny used to do, I would (perhaps rather pettily) include the following:
Piling up the rubbish in a huge pyramid on top of the binbag so she doesn't have to change it yourself.
When the pile topples over, scatter carrier bags full of rubbish from the kitchen bin randomly around the overflowing bin (so someone else will deal with the mess and not her...)
Diluting the washing up liquid (an Eastern European thing I think)
Removing the cardboard tube from the loo roll holder and chucking it on the loo floor, but not bothering to move three feet and replace it with a new loo roll.
Saying "It depends what you're having" when you ask if she will be eating with the family that night.
Dumping clothes in a crumpled mess on top of the tumble drier so she can get her stuff in it, instead of folding it so that it doesn't need ironing.
Having to be asked every week to do one simple thing (eg use the brush when you've had a poo, put the children's clothes away if they're clean and folded on top of thewshing machine...)
Feeding children processed crap that she has bought herself (eg microwaveable burgers) rather than grilling fish fingers and making mash to go with them (too much effort).