Apparently, this is attributed to the idea that women are much more negatively affected by objectification than men, to the point that it screws up their attention and cognition. For men, they were actually proud of strutting their stuff, and so a tiny Borat-style mankini actually increased their abilities.
Now, before you run off and declare yourself ready to perform surgery just because you bought a set of surgical scrubs, stop and think about what this study really found. It's not about fashion's influence on your brain, it's about how flexible intelligence really is, based on your emotional state, your ability to focus and God knows how many other factors. After all, one reason intelligence is so hard to measure is that it's not like measuring somebody's height. Your intelligence changes based on what day it gets tested, the setting and mood you are in, how distracted you are and (as this study seems to imply) what you think is expected of you.
And, we bet if you think back, you'll realize that all of your best teachers in school knew that last one very well.