Today male breast enlargement (Gynecomastia), is a very common condition with men. It can result in teasing, horrifying embarrassment, and social distress. Many men try to hide it with thick shirts, avoiding bare chested activities, and withdrawing from public contact.

Why Men have nipples

Without Nipples the Male Chest would look strange. They direct the eye to the curve of the pectoral muscle.  

Men and women are mammals (from the Latin mamma breast) a species that have breasts and feeds its young with milk. The human embryo has tissue that evolves into breasts. Both female and male babies are born with nipples and ducts intact. It is the presence of genes that direct hormones to differentiate the breast tissue. The Y chromosome stimulates hormones such as testosterone to form male features. 

Insufficient or defective testosterone, poor tissue responsiveness, or an unbalance of other hormones like Prolactin and Estrogen can cause female like breasts even in men (Gynecomastia). At birth, the small amount of the mother's estrogen in the baby can result in small breasts they usually resolve. There can be an unbalance of hormones during male puberty that can result in some temporary breast growth, this resolves for most. There are many medical problems and drugs that can cause male breast growth. 

The nipple is actually the central protrusion inside of the pigmented areola. There is a thin muscle just under the skin that when stimulated, tends to flatten the puffed male nipple areola. This muscle when stimulated in a breast feeding woman, projects the nipple for the baby. Nerves that innervate the nipple / areola can produce pleasure for both men and women. The male chest without nipples has an unusual look. Long nipples can also be a problem.