We are mostly descended from the underclass. That's one of the reasons we tend to get so irate when somebody gets "snooty".
But an undercurrent of that is a fairly continuous worry that we're overstepping our bounds. Very few Americans I know are immune to it, though reactions to it vary. Some people are timorous, some overcompensate by being boisterous and overbearing, some accept it to the point of attack [tourists in Madras-plaid Bermuda shorts]; but there's always some evidence of our class origins, and a little nervousness that we aren't behaving quite correctly or don't know the fine points of etiquette in situations.
Which is ridiculous. Two hundred and twenty-four years; Great Britain has been a country, with no hiatus, for longer; how many more such are there? In point of actual fact, we're not a young country any more -- we're quite an old country. La belle France? Pooh. Not even sixty years; why are we listening to these parvenus? :-)