not really, it could just happen later on in the development process when the gender is already determined.
though I agree that we probably won't lose our nipples unless we drastically evolve physically. But at the moment nipples on guys aren't needed but they aren't really doing anything bad, so there is no reason for them to not be there.
I'll have to go with this. Species typically lose certain features because they provide some kind of disadvantage. It's why we have appendixes and whales have pelvic bones despite both being useless: they provide no disadvantage at all, so their carriers will still breed and pass the traits. On the other hand, if someone grew with a freakishly large slab of useless meat on them 10000 years ago then they would be eaten by wolves/bears/lions and would be purged from our gene pool. In short, humans will not lose their nipples because they provide no disadvantage to us (and even if it did we would still keep them alive, basically giving the finger to nature and natural selection).
Since men have breasts, they can get breast cancer. The outside part of breasts are the nipples... so if we evolved to have only muscle there with little fat or hormonally effected tissue then men would not get breast cancer, therefore it is an evolutionary reason for men to not have breasts, and by extension nipples. But this probably won't happen.
More importantly: Appendix. More dangerous than male-nipples and just as useless.
The whole idea of losing specific parts is that the carrier of the gene needs to die before they can breed. We have surgeries to remove the appendix and people typically have children before they die of breast cancer.
