Wiktionary
n. (context slang English) A cramp-like ache in the testicles and prostate region caused by prolonged sexual arousal.
Wikipedia
Blue balls is a slang term for the condition of temporary fluid congestion ( vasocongestion) in the testicles accompanied by testicular pain, caused by prolonged sexual arousal in the human male without ejaculation. The term is thought to have originated in the United States, first appearing in 1916. Some urologists call the condition "epididymal hypertension". The condition is not experienced by all males.
Usage examples of "blue balls".
Little Nemo walks around with a seven day hard-on and a wonderful pair of blue balls bequeathed by Lady Bountiful.
She had pushed me away and clapped her knees shut, had told me she was going away just when I was starting to not only want her around but need her around, she had left me with what was soon going to be a world-class case of blue balls .
Her toothless mouth worked craftily at the cigarette held there, blowing out puffs of blue smoke that seemed to hang above and behind her in little bunched blue balls.
Buddha's blue balls, you dildos couldn't remember your numbers if you had them tattooed on your foreheads.
It was more like Buddha's blue balls locked in Mohammed's pointed teeth!
To his amazement he saw that the cattle seemed to have caught the lightning--little blue balls of it rolled along their horns.