why do guys..............

[slipper]

why do guys have nipples?

[macka]

You have issues buddy.

Men, or humans have nipples because it identifies us as mammals.
Two features distinguish us as mammals, hair and nipples.

So that's why we have nipples. OK?

[CrackedButter]

Nipples develop in the womb before our sex does. Once the sex has been determined the nipples start to act accordingly 9 years later, swell up or do nothing.