A post-doctoral researcher in the psychology department at University of California, Berkeley, conducted a number of studies that show people with more money are more likely to be rude and break rules.

“Americans may be more narcissistic now than ever, but narcissism is not evenly distributed across social strata,” the researcher, Paul Piff, wrote in a paper that explained why “higher social class is associated with increased entitlement and narcissism.”

Piff and some of his colleagues have conducted a wide range of studies that show the attitude differences between people with more material wealth -- even if they didn’t earn it -- and individuals who lack wealth.

“As a person’s levels of wealth increase, their feelings of compassion and empathy go down, and their feelings of entitlement, of deservingness, and their ideology of self-interest increases,” he said in a Tedx Talk in Marin County, Calif.

One study involved two players who don't know each other, a rigged game of Monopoly and a bowl of pretzels.

The setup: The two strangers are told to play a regular game -- except the rules are slightly different than usual. One player starts with twice as much money than the other and an extra dice to roll.

In every case, the players recognized that the game was rigged, but as time went on, the “rich” player became more rude and obnoxious. That person spoke and moved louder, and even ate more snacks than the other participant. When the “rich” spoke about why they won, they would focus on their own strategy.

“They became far less attuned to different features of the situation, including that flip of a coin that had randomly gotten them into that privileged position in the first place,” Piff said.

In another experiment, he looked at different levels of generosity. Piff gave a variety of volunteer participants $10 and told them they could keep it or share part of it.

It turns out those who had lower salaries (less than $25,000) gave 44 percent more to the stranger than those who made more than $150,000.

Piff also studied footage of a crosswalk in California to determine that 50 percent of people in the most expensive cars would not stop for pedestrians, while those with the cheapest cars stopped every time.