Metaphorically used to suggest something is aesthetically pleasing to the point where the groin feels pleasured, despite the lack of physically stimulating the groin at the time. In reality the groin does not feel pleasured, but use of the metaphor exaggerates the aesthetic pleasure gained from whatever it is that is being described as 'groinulating'.
"What do you think of that new song by Noel Gallagher?"
"I think it's groinulating!"
"Me too, what about that new Justin Bieber song?"
"Oh, that's a load of shit!"