This is a really interesting issue.
When I was 17 years old and was dating my high school sweetheart we both had a fetish for each other's underwear. We would switch underwear each week after we washed them, she would wear mine and at the end of the week give the dirty ones to me so I could wash them. And I would wear hers and at the end of the week give them back to her to wash. Our parents never had a clue as to what we were up to so we continued to do this for two years.
Well it is now 13 years later and we are married and have two children and continue to shop together for underwear. But the interesting thing is we masterbate together while we are wearing each others underwear and we really enjoy doing this together. I will never buy guys underwear again I love the satin and silky panties as well as the lace string bikinis. The two of us really love to masterbate first thing in the morning so all day long we can feel our cum against our shaved pubic area. Also the smell is out of this world as the day goes on it makes you really look forward to getting home to have sex.