The final moments prior to when a man orgasms. At this point he can no longer stop himself from ejaculating no matter what happens. He will make a face as though he has just smelled vinegar. It is said that if you peer into a man's eyes during his vinegar strokes you get a glimpse of his soul.
Justin and I accidentally walked in on Kyle during his vinegar strokes. Now we know things about him that no other person can.