The rule that a man must warn a woman when he is about to ejaculate during a blowjob, so the woman has proper time to get away from the ensuing explosion of man juices. Many men do not follow this rule, prefering to make their partners suffer the onslaught of being choked by their thick, ejaculatory fluids. A common misconception is that the majority of women enjoy being drowned in semen. Although some actually do, many do not, and instead will either allow the fluids to be released on their faces, or they will revert to the handjob position and finish the job in a more comfortable, safe area.
"Everytime Jane gives me a blowjob, she reminds me kindly of the unwritten blowjob rule and then proceeds to get a safe distance away from my cumshot. Sometimes when I am lucky, she lets the cumshot hit her in her face."