What are blue balls?

From: [email protected] (Jim Markley)

Blue Balls is a real condition! The "correct" term for blue balls is
epididymitis, which is an inflammation of the epididymis. So what is
an epididymis, you ask?

Well from the library dictionary -- an elongated mass at the back of
the testis composed chiefly of the greatly convoluted efferent tubes
of that organ.

In simple terms blue balls most commonly occurs when the epididymis
get blocked up when the sperm leave the testis but not the penis.
The "efferent tubes" are the conduit for the sperm from the testis to
the urethra. When they get blocked you get pain. Why blue balls and
not "swollen balls," well maybe the connotation is that you balls have
the "blues", or maybe its because with all that swelling some of the
blood flow is restricted enough to cause some blueing of the area
because of pooling blood.