In support of the answers above'. It is human brains that regard nipples as being sexual, not the human body.
At conception, our bodies are given two different types of chromosomes: one type that determines gender and the other type that builds the relevant bits that apply whatever the gender ' brain, heart, and so on. Nipples come into the non-gender related category. So the basic functioning bits are given immediately ' regardless of what gender we may be given. Although as we develop, the growth of these organs is influenced by the gender chromosomes, but not initially created by them. In other species of mammals, the males do not have nipples. Why human males have them is unknown ' they have never been a 'working tool' in men, and claims that males may have suckled young millennia ago are thought to be rubbish.