But because I am a scientific person, I think it necessary to answer this question with logic instead.
During formation in the womb, all human embryos, regardless of sex, develop parallel mammary ridges called milk lines. These milk lines develop in the chest area before the 23rd chromosomes (XX or XY) work to develop the physical traits that distinguish a male foetus from a female one. As the foetuses develop the milk lines slowly recede, leaving behind a pair of nipples and breast glands that are capable or producing milk in both sexes. That's right. Men can make milk.
Interestingly though male mice do not have nipples! Why? Because they have evolved a little more than us mere humans. Yale researchers discovered that while male mice go though a similar mammary development process, they also go though a secondary transition that removes the nipples. After a few days in-utero a protein known as PTHrP signals the mammary cells to form male hormone receptors which destroys the breast tissue, leaving the rodents smooth chested and completely nipple-free. Eat your heart out anti-Darwinians!
So basically, men have nipples because women do. Like I said. Men were made in God's lady image.