When two individuals engage in oral sex and the beard of the gentleman tangles itself with the pubic hair of the woman. Usually acheived while in the sexual position of sesenta nueve, that's 69 for all you non-hispanics.
"Ouch!" screamed Gertrude...
"Whats wrong?" Leonard asked.
"I think have ourselves a naughty knot" she replied.
Some hairy bitches never learn.