The point during sexual intercourse at which the male ejaculation is imminent. The only course of action left to the man is where to deposit his manseed.
"I was railing Anna last night when she mentioned Battlestar Galactica. I immediately reached ejaculatory inevitability and blew my dewshot in her face."
The point during sexual intercourse where the male realizes he is about to cum (ejaculate) no matter what he does to stop it. Usually at this point semen has already entered the base of the shaft of the penis, so the male cannot stop the ejaculation process no matter how hard he tries.
Grunting and groaning and kegeling didn't help he had cum up his shaft and he was at his point of ejaculatory inevitability.