I'd agree with what most have said so far. Topping from the bottom can occur in a number of ways, from the extreme and obvious pointed out by bambina to the slightly less obvious but equally damaging subtle approach pointed out by MacGuffin. Essentially the submissive takes control away from the dominant, maintaining the power, and shifting the process into a Top and bottom dynamic rather then one between a Dominant and submissive. And it is worthy to note that the term is often thrown about by inexperienced Dom/mes to describe strong willed subs who aren't afraid to speak their mind, when in fact that is a failure of the Dom/me to remain assured in themselves and their power in the situation. That isn't to say that being outspoken to the point of "brattiness" can't be topping from the bottom. I believe this is what MacGuffin is referring to. The idea that a submissive will think somethink like "I would really like a spanking." So, the submissive remembers that the last time she did [insert action] the Dom/me responded with a spanking, and so she goes and does that action to try and receive a spanking. Here she has basically tried to manipulate the Dom/me into giving her what she wants rather then being honest with the Dom/me and requesting a spanking and leaving that option up to them to decide if/when/how that spanking would be administered. Just my two cents.

Cheers, Myst