- If the city does not have a Chinatown, there are no Tongs or Triads.
- If the city is Miami, you should learn the word "cartel" or you will catch a bullet.
- New Jersey and New York? Parla italiano o muori.
- Unless it's The Roaring '20s, in which case Yiddish will come in handy (although it can't entirely replace Italian), or the 1850s-60s, when, unless you can trace your ancestry to the Mayflower, it would be advisable to learn Gaelic.
- Even then, you'd be better advised to spruce up your Russian alongside your Yiddish before going anywhere near the vicinity of Brighton Beach.
- Additionally, there's parts of town where you better be down to speak that Ebonics. Harlem, certain parts of Brooklyn, and Newark especially. Spanish will come in handy in other parts of the same areas, although a lot of the time the Spanish speakers will be civilians.
- Chicago: You can speak Italian or Gaelic. Just don't let the Yiddish guys hear you, unless you have a deal with the Italians. Don't forget to watch out for the Polish folks, as well: they own the town. And white folks: do not presume that you have N-Word Privileges anywhere in the South Side, because you will find yourself six feet under with all the other presumptuous crackers.
- Los Angeles: Speak Spanish, and learn the difference between "barrio" and "narco". In certain parts of the city and in the surrounding countryside, men on motorcycles are not your friends. You will also need Chinese, Japanese, and Russian, too, and Ebonics, plus others you'd never considered (Armenian?). You know, really, you should just keep quiet.
- Baltimore: Ebonics
- Philadelphia: Ebonics and Italian. Remember how "they blew up the Chicken Man in Philly last night"? That's the Mafia.
- Speaking of that song: Atlantic City, New Jersey: Ebonics in the hood, Philly Italian historically and near the casinos.
- Providence, Rhode Island: Gaelic, Italian.
- Boston: Mostly Gaelic, but the occasional Italian or Ebonics thrown in for flavor.
- Detroit: Mostly Ebonics, but you'll hear snatches of very menacing Italian and occasionally Greek. If you plan on hanging in Highland Park, learn Hmong. The ones speaking Arabic (Chaldeans, mostly) and Armenian look menacing, but are completely aboveboard and harmless unless you plan on knocking over their store/restaurant.
Metro Specific Underworld
Underworlds are ethnic. It says so right here. Furthermore, the ethnic underworld in effect is specific to the American locale of the setting.