I wrote a hub on this previously. Of course they are aware of it. It doesn't matter if fat or skinny; bootylicious or barely there. First of all, its tacky when women do this, but its worse with the men because without fail it is always the fat sloppy ones that are showing plumbers butt that you REALLY don't want to see!
However, it is more annoying when women do it, or allow it, because I can tell you that EVERY time my pants drop to where something could be showing, I know it, and immediately pull them up. And yes, they can feel the breeze. I had a pair of hip huggers that I was fighting with every time I sat down because it could it slide down & I could feel the airflow, even while in my car, which is why I was fighting with the pants to pull them up prior to stepping out of the car.
Let's just face facts. The people that walk around like they are oblivious simply don't care, are people of low class and reputation, or are exhibitionists.