In a Nutshell
Although schwenkel sounds like a Yiddish euphemism for a gentleman’s nether parts, in reality, it was just part of a medieval knight’s panoply. The schwenkel was a long banner at the top of a knight’s banner. Whether it constituted an honor or a disgrace is disputed.
The Whole Bushel
In the Middle Ages, knights were highly skilled warriors and war leaders serving the king. A “knight banneret” led troops into battle and was granted the privilege of carrying onto the field his own personal, square banner depicting his heraldic arms.
Sometimes, a longer tail or thin ribbon of fabric was fastened to the top of the banner—a schwenkel. The schwenkel could be a yard or longer. Red was a common color. The name may derive from the German schwenken, meaning “wave,” as in waving a flag.
Historians disagree on whether displaying the schwenkel was an honor given to a particularly talented knight, or a disgrace marking an incompetent or disfavored knight. The word may occasionally also refer to the whole banner with the long tail attached.
Show Me The Proof
Zürich canton (Switzerland)
North American Vexillogical Association: Dictionary