Definition & Meaning of "knob polisher"in English

What is the origin of the term "knob polisher" and how is it used?

"Knob polisher" is a British slang term from the late 20th century, combining "knob" (penis) with "polisher" to create a metaphor for performing oral sex on a penis. It appears in sexual slang, explicit humor, and pornography. The term can be descriptive in explicit sexual contexts, but it is often used as a crude insult implying servility or humiliation. Its tone is vulgar and context-dependent, ranging from explicit description to deliberate insult.