It saved the life of Vicki Parsons, a 26-year-old british woman who had a boy approach her while sitting in the car and try to stab her. The blade caught on the underwire of the bra, and only allowed the point of the knife to cut her.
So, according to the Telegraph, the bra literally saved her life. She reports that it was only $12 at her local store.
So while they can be unpleasant to wear, and darnright uncomfortable to slip your hand under on a hot date (while still hooked in the back), you may want to reconsider it.

