Someone who wants to put up a fight in bed just to lose it and be railed senseless as a "punishment", except it's not really a punishment because it's exactly what they wanted.
Brats are, in essence, naughty submissives. They find disobedience a form of playfulness rather than letting their dominant down, and require a compatible dominant who will not only teach them a lesson, but also accept that any number of lessons might still not necessarily change this behavior.