I see Topping fro the bottom as when the sub deliberately manipulates the top to get what she/he wants.
Not just making requests or having an opinion, but trying to make things go her way, instead of what the top intended.

Personally, I do it sometimes and it's a habit I'm trying very hard to break.
When I get away with it I end up feeling unhappy about it, since overall getting what I want isn't really what I want, but it's so easy to try and squirm my way out of something unpleasant. It's much better when he catches me and calls me on it.
It's different from playful brattiness, where we both know that I'm just being a tease to get a reaction and he may or may not indulge me.

*shrug* of course that doesn't apply anyone except me, that's just what TFTB is to me & my relationship.