What does ‘Cocktail-party fool’ exactly mean? Is it established English word?

I found the word ‘cocktail-party fool’ in the following sentence of the article in the Book review section of the New Yorker (August 16), which is titled ‘How Do You Say Ralph Fiennes?’

“The mini-videos are essential viewing for people fearful of making a variety of conversational missteps that would immediately peg them as philistines, charlatans, or general cocktail-party fools.”

As ‘Cocktail party fools’ is laid in parallel with 'philistines' and 'charlatans' with antecedent ‘or,’ the author seems to have used the word as a synonym with philistines and charlatans. But naturally there should be difference among all three words. Though I can deduce the meaning of the word from its word elements, what does ‘Cocktail party fools’ exactly mean? How different it is from a ‘Party-pooper’ who is ridiculed by others by making an illiterate remark at a party?’

I checked the definition of ‘Cocktail-party fool’ on online dictionaries. Neither Cambridge nor Merriam-Webster online dictionary registers this word. Is ‘Cocktail-party fool’ an established English word, or the word just in making?

Solution 1:

No! Googling quickly confirms (only 5 hits!) that it isn’t an established phrase.

So what does it mean, as the sum of its parts? Someone who is a fool at cocktail parties. Why cocktail parties specifically? Cocktail parties have long been used as a byword (at least since the days of Thurber) for small-talk and superficial conversation — especially, superficially intellectual conversation.

So a cocktail-party fool is someone who makes a fool of themself in superficial conversation, by attempting to show off their knowledge but, in the event, proving wrong.

A party-pooper, by the way, is something rather different: it is someone who tries to stop other people from having fun — for instance, the neighbour who knocks on the door at ten o’clock and asks you to all stop talking so loudly.