A thin, usually black net, put on the head, used to keep the hair tight, avoiding spillage, food contamination etc. Used by chefs, cooks, waiters etc., also sometimes used by people with wigs.
When the person you just penetrated is in an unconscious state you grab the condom you were just using and squeeze out the jizz that remained, and then mess around with their hair so when they wake up theres dried out cum all over their head and it looks like a hairnet. (Works best on brunettes)
The sad condition when men with average sized genitalia exit a lake or other cold body of water and have their miniaturized package trapped by an entangled mass of pubic hair.