As long as it doesn't harm you or anyone else -- for example, you don't steal them because you're too embarrassed to buy them or you wear them as an outer garment to work in violation of dress codes, thus risking getting fired -- then there's nothing wrong with it and it's nobody's business but yours and maybe your partner's, if you have one. Wearing clothes of the opposite gender is considered harmless as long as you do it in a way that causes no harm. Right now, I'm wearing a man's shirt. Nobody blinks twice at that. If a woman can wear a man's shirt, I don't see why a man can't wear a woman's silk slip or other undergarments. Who's to even know unless you show or tell them?