The knee was invented in the 1990s by an elite sexual group of american gingers. Some misconceptions about the knee is that a girl can get pregnant from the knee, and that the knee can transfer sexually transmitted diseases.
When using the knee the most common mistake is to use excessive force as well as slamming the knee into the vagina. While some vaginas are leathery and can handle excessive slamming action, most are tender and can be damaged permanently.
Girl 2: Let me guess, Chad performed "the knee" on you again didn't he?
Girl 1: Yeah. :(
Girl 1: Wow I feel amazing today.
Girl 2: Why, did you get a good kneeing last night?
Girl 1: Hells yes!