It is probably unfair to throw all of these in a single despicable category, but the abuses in the last 40 years are so egregious that only a complete moratorium on all mansard roofs will suffice to still the repulsion of most architects.
A mansard roof is unusually a full story of a building masquerading as a part of a roof. It is a gambrel/hip roof hybrid that brings the apparent mass of a building down a story or two by letting the "roof" start much lower down than the interior floor levels would typically indicate. Handled well they are a pleasing architectural solution to a vexing problem. Most often however, they are not so deftly deployed and instead of reducing the apparent mass of a building, they increase it with a gargantuan, bulbous forehead. These are not attics with quaint dormers sticking out, but rather massive toques with eyeholes sitting on top of otherwise rather elegant buildings. Or maybe not so elegant.