Lots of these answers point to people with money, but I consider the Upper Class to mean generational wealth. One is crass and one is class: Different games.
Real UC behavior: Having global connections in certain circles (the UC know each other because theirs is a very small world). Being incredibly cheap while doing activities and living a lifestyle that isn't accessible. The upper class values frugality not flaunting brandnames. They will try to save money on their year long ski lift tickets, relish in stealing hotel toiletries, brag about their recent deal on a vintage Shelby, and extoll the virtue of custom made ("quality lasts forever, cheap is more expensive in the long run!")... scrimping on the little things with their 99c coffee while purchasing three hundred head of cattle for the ranch in Wyoming. Nothing to me screams UC more than a worn out pair of Tods loafers, or the 1994 truck you keep at the country house. Frivolity is traditionally frowned upon.
The UC folks probably know that guy who ripped out his 80k cabinets after a couple years, but he is a punchline at parties, not "people like us," and it will be a generation or two before that changes. But, hey, to each their own.