Very interesting men are hiding their nipples these days - men are generally shy to show their nipples ( "nipples" otherwise known to Otaku as "B-chiku"). Even if its just their B-chiku showing through a t-shirt.
These products are made for women and recently they are making them for men. Done a search to find this product called Nippless ( 526 yen for a 6 pairs - which will last you 12 times if you have only one nipple) which is for women *and* men (the kanji 男女兼用(だんじょけにょう) on the packet means "for men and women use").
Are you shy of showing your B-chiku? Would you use this product? And why the hell do men have nipples anyway?