I think it is because the body had a mechanism so piss and cum don't mix - the chemical environment isn't good for sperm. So your body might need a while to turn it off.
I think there was a Jim Carey movie where he had a scene where the guy couldn't piss right after sex, but because he had memory loss, he didn't know why he couldn't piss right.
If that mechanism doesn't exist, then the rest is crap and you just grip way too tight.


