Q:

What is the correct usage of arriviste/parvenu?

In one of the episodes of the TV show Rosemary & Thyme the word arriviste/parvenu was used.
Context how it was used: Person A considers person B as an arriviste/parvenu.

Person A is rich and has been growing orchids all his life.
Person B recently starts growing orchids.

My question is, can the words arriviste/parvenu be used for making political accusations? In the following context, Politician A considers Politician B as an arriviste/parvenu.

Politician A: very senior
Politician B: new to politics

A:

I think you're guessing well at the origin of the words, because how you seem to be interpreting them is close to their original French meanings.
However, often loan-words are borrowed to serve a particular purpose only and so have a narrower meaning in English than the original form. (The inverse can sometimes happen too).
Arriviste and Parvenu both describe someone who is "new money"; wealthy but without the social knowledge that allows one to fit into the social class of those who've enjoyed a similar level of wealth all their lives.
Both terms are used from a class-conscious position where the terms are negative because such people "don't know their place", or at the very least are so lacking in "class" that they cause embarrassment.
Arriviste is perhaps a bit more aggressive in this than parvenu, but neither are nice things to call someone.

Can the words arriviste/parvenu be used while making political accusations?

Yes, extending the word to figuratively cover the political sphere, but you would have to do so from a distance, and even then it would be fraught.
The terms are associated with a snobbish attitude, and so while a pundit might get away with it they might also just seem prejudiced and anti-democratic. A rival politician would be much less likely to get away with it, because opponents would be sure to seize on it much as when the British Government Chief Whip was forced to resign after allegations that he called police officers "plebs".
You couldn't get away with it in public, but you might in private among some like-minded friends, but really you'd only be likely to do so if you actually were a bit of a snob anyway.

