Definition: someone who has newly attained a high position, but not general social or professional acceptance
See also Parvenu.
Why I Looked It Up
Ann Coulter turned on Donald Trump and was quoted as saying:
I grew up in New Canaan and I’ve been reading Page Six since I was a little kid. I was well familiar with what a narcissistic, ridiculous, tacky, vulgar, arriviste this guy was. That I knew about. The one thing I underestimated, in fact, did not see at all is, I had no idea how abjectly stupid the man is.