knee sex is when while making out with a guy(laying down), he carefully rubs his knee against a girl's crotch to stimulate her vagina and get it ready for fingering and/or sex.
girl 1: I wasn't going to go past 2nd base with him, but he started doing something with his knee and i went crazy.
girl 2: O he did the knee sex move. yea he does that well.
Very careful targetted groping of the knee, as well as under, below and above the knee to achieve knee-orgasm. Preferably performed by more than 2 people (gender is not an issue with knee sex)
When a male and female are aroused the male takes his enlarged penis and sticks it behind a woman's knee and beats to his own rhythm
Jack and Emily are naked in bed so emily sands up and jack whoops out his fat cock and sticks it behind her knee and moves his torso back and forth and thts knee pit sex
Short-hand for the word floccinaucinihilipilification, meaning the estimation of something as valueless (encountered mainly as an example of one of the longest words in the English language).