Nipple pain in adolescents is common and normal. Pain in the nipple in an older man deserves investigation.
A great deal depends on whether the pain is in the nipple itself, the tissue beneath or the ribs. If you suffer from arthritis, the ribs can be painful where they join the breast bone. Pressing on the rib through the nipple will trigger this pain.
If it is in the tissue under the nipple you may have a chronic infection which can result in a cyst. These are often tender and painful. Pain at the nipple itself may be from infection or constant rubbing against clothes.
You should consult a doctor just to be safe.
Would be nice if I posted more important information. White male, 38 years old. No swelling or discharge. Just the extreme pain. Any answers?