noun.upstart, newcomer, late arrival, nouveau riche, parvenu, generally characterised as an ambitious, brash or arrogant person who has yet to integrate with his or her new social group.
WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
noun.
a person who has suddenly risen to a higher economic status but has not gained social acceptance of others in that class
Word Usage
"The supreme need of the arriviste is to be able to disown and forget those who have helped him so far."