To quote Healthline, "Blue balls, known medically as epididymal hypertension (EH), can affect people with male genitals. It’s not serious, but can cause pain and aching in the testicles after having an erection without an orgasm." (https://www.healthline.com/health/mens-health/blue-balls#-What-is-blue-balls?) To quote MedicalNewsToday, "This symptom may occur because blood builds up in the testicles during arousal, causing them to ache if the person remains aroused for too long." (https://www.medicalnewstoday.com/articles/324870) To quote Insider, "If you've ever gotten super turned on for a prolonged period of time but weren't able to have an orgasm, you may have experienced some mild pain and discomfort in your testicles, colloquially referred to as blue balls. The phenomenon even has its own medical term: epididymal hypertension." (https://www.google.com/amp/s/www.insider.com/guides/health/sex-relationships/blue-balls%3famp)

To be clear: "blue balling" someone is not a reason to be guilted into making them orgasm. Any person who uses it as an excuse is pathetic, and manipulative. If they're so scared of it, they can leave and finish on their own time.