Want to avoid embarrassment when visiting U.S. cities? There's a great series of posts on Q+A site Quora (a social question and answer site similar to Yahoo! Answers) discussing cultural faux pas to avoid in various cities.
Some of the tips are serious (pretty please, don't stand on the left side of an escalator in Washington!) and some are just funny riffs on the stereotypes of the city. Either way, they're lots of fun and a good way to end the week. Here are some of my favorites.
Quora asks: What are some cultural faux pas in...
Washington, D.C.
Tour buses. Yes, in general.
Although this person also adds the very nice caveat...
I don't want to give you the wrong opinion, area residents generally like tourists or at the very least understand that they are a vital part of what makes D.C. cool. Just don't be that tourist, you know?
San Francisco, C.A.
Complaining about the fog. It has been here longer than you. It will be here when you are gone. San Francisco has been called the "Cool Gray City of Love". Just dying to complain? You may mention parking - briefly.
Detroit, M.I.
Don't put ketchup on a hot dog. Chili, onions, mustard, maybe even cheese, but never ketchup.
Alabama (the whole state, but Birmingham specifically)
Don't ask someone to "say something". I receive this request every time I travel abroad. We as Southerners know our accents can amuse non-Southerners, but remember that 1) not all of us have accents, and 2) we don't exist for your amusement.
Bonus: One thing that's surprisingly NOT a faux pas...
New York
Feel free to interrupt someone who is speaking to agree with them. This is considered polite, if occasionally annoying. Don't be frightened.
You can also take a look at answers for:
Seattle
San Diego
Chicago
Los Angeles
New Jersey
and several global cities as well!