there is a book by this same title so you can buy it on amazon and get the answer first-hand. without nipples how would teenage boys torture each other with "twisters"? what would punk guys have left to pierce? how would you know when it was cold? nipples in men have no medical purpose but since it hurts to remove them and you will look a little weird without them just leave 'em alone. maybe another few thousand years of evolution will make them disappear.
why do men have nipples? . we know that women use their breast for breastfeeding. men get breast cancer but what is the purpose of men having nipples.