Complex sentence: The term was once prevalent in Parisian circles, applied deprecatingly to those who professed allegiance to the Socialist Party, but who maintained a far from proletariat lifestyle that distinguished them from the working-class base of the French Socialist Party.
Split into simpler sentences: The term was once prevalent in Parisian circles, employed deprecatingly to those who professed allegiance to the Socialist Party, but who maintained a lifestyle that was visibly non-proletariat. Which clearly distinguished them from the working-class base of the French Socialist Party.