Ohh!  I don't think my gym allows sports bra in the weights/cardio area but its def. OK in the yoga studio room, especially since its 90 + degrees for the hot classes.  Fats often come to my power/sculpt classes where there are plenty of mirrors for them to see people around them, and themselves!  I'm a big believer in technique and breathing well and I was taught to squeeze my abs at the end of every exhale to clear out the lungs.  It  took lots of practice to make it routine but its made my six-pack!  The fats don't have the discipline to breathe correctly yogi style which is why they run out of energy and take lots of breaks.  Its in those glorious moments that I usually catch one of them staring at me and if its an evil eye all bets are off.  The bitch is about to get a lesson in motivation.