When the depth to which your cock plunges exceeds the comfortable limits of vagina into which it is thrust and hits cervix.
Also known as the “YOU MOTHERFUCKER!!!!! Fuck, Daddy.. Do it again please????”
Normally, its just something that happens, but during rough play it can be bad. I wound up with a bruised cervix doing this and it was one of the worst things of all time. It hurt real bad and it took two weeks to fully heal, which also means no sex during that time. Yeah, that was like agony, and I can only give nothing but blowjobs for so long