noun \ar-ee-veest; a-ree-veest\
A person who has recently acquired unaccustomed status, wealth, or success, especially by dubious means and without earning concomitant esteem.
An ambitious or ruthlessly self-seeking person, esp. one who has recently acquired wealth or social status.
I was going to draft my own arriviste sentence, but I think I'll let the above picture and Merriam-Webster's example speak for themselves.
The town's old money immediately shunned these vulgar arrivistes, who may have had the cash but certainly not the class.