A bra because generally, men don't have a physical need for it. As well as heels, stockings, lace or a corset because modern culture has assigned that the females. Taboo is a stigma practiced within a society. If you feel compelled to cross dress, first visit a safe place it's accepted. You can't expect the people around you to change for you, a large part of the U.S. is still unwilling and very closed minded to "alternative" lifestyles.