A term, which came about in the 1800'
s, however became
popular with soldiers in the Second World War.
A knee knocker is a specific act of casual sex, usually performed in an alley beside or behind a
pub/bar/tavern.
The act is performed standing up, with the
woman secured against a wall with a combination of the
mans upper body and holding her buttocks. The womans legs, usually wrapped around his waist.
This unusual position, whilst having sex results in the knees of the male regularly knocking together (often with some force), hence the term.
Also refer to the term 'knee trembler'.
Grandfather: "Whats the
name of that young lady you went to the movies with last night?"
Grandson: "Michelle."
Grandfather: "Arrgh, I met a girl when I was serving in
France, called Michelle. We had a knee
knocker behind a cafe in Rennes."