It's because whereas I am all woman, you are only half woman. So you have boobs but they are useless...
I think it's because God was sitting there looking at his creation one day and said, "hmm...I feel the man needs something useless on his body...the bellybutton just isn't cutting it." Then BAM! Nipples!
It's not always a straight cut as the whole X verses Y explanation. Some men are born with a XXY, XXXY, XXXXY and so on chromosomal make up and some of these men have evident breast tissue and even can lactate.
all nipples are for clamping! fine specimens.... classic clamp.... attach to car battery, or use adapter to plug into standard household socket for electrifying sexual experiences....
Men can also get Breast Cancer. Go to any Susan G. Komen event and you'll see at least three guys who had it. I only know that because I've made it my personal life goal to save the ta-tas.