A phrase intended to imply that someone needs to calm down or relax. Spanx are a slimming body sleeve that women wear. Saying this to a woman implies that she is fat and being annoying or overreacting. Saying this to a man implies that he is a woman, fat, and overreacting or being annoying.
Coined by C. Tonsmeire 03/10
"Chris, can we switch over to that cooking show?"
"Jesus, Dave, don't bust your Spanx. I'll change the channel at halftime."