Possible Clues:

• Person suddenly risen in world, and arrogant
• Trat's without a backround
• Unexpectedly fresh version of The Great Pretender?
• Social climber's advantage following successful period
• Person who has risen quickly, and arrogant with it
• Society crasher
• Recent promotees, say, behaving with arrogance
• Trat's without a background
• Person who behaves arrogantly in the new position
• Trat's just got there