Boy, those French. They have a different word for everything.
I wish I could recall the name, but I recall reading of one highly dysfunctional, self-destructive tribe whose culture pretty much consists of constantly trying to ruin each other; socially, personally, materially. They live in crude conditions even by hunter-gatherer standards because no one can build and keep anything without someone stealing, breaking or tearing it down the moment they aren’t looking.
They and other dysfunctional societies are going to be the winners of any “most inconsiderate and selfish” competition; given that places like Germany and so forth still function they can’t be as bad as a culture/subculture that has torn itself to pieces.
Those are called “graduate students.”
Those are three different things (blunt, rude and selfish).
Japanese communication protocols favor surface politeness, but they can slice you so neatly you don’t feel it for an hour (especially women, especially middle-aged women). It isn’t only those swords that are sharp. So they aren’t blunt, but they can be very rude if they want to be. Considerations of the feelings of others mostly only happens for people of high status or who rank over you (i.e. people who can do you good or harm).
Selfish is something else again. I don’t think that’s a cultural trait.
Roddy
In Deaf culture, people tend to be more blunt than non-Deaf.
I don’t know why; they may be self-effacing in general, but if you’re in the least bit overweight they’ll repeatedly point it out.
self-loathing americans are amusing.
Quebecois?
Classic Gallic snootiness, world class hagglers and an icy disdain for anything Anglaise related.
Disclaimer- I am not widely traveled, North America only…
Isn’t it the “New York Urban” culture?
“You Hump!”
Koreans are pretty rude by Western standards. They think nothing of pushing you out of the way without even an “excuse me.” They never hold doors open for the person behind them. Middle aged men hawk up loogies really loudly in the middle of the street. Middle aged women will berate total strangers if they see fit. A friend of mine (a foreigner) had her baby here and she was taken aback at how people would just pick the baby out of his stroller without even asking her if it was okay. Serious boundary issues.
They can be quite warm and generous if they like you, though.
As others have said, rudeness is subjective. Spanish people are really rude to strangers, by American standards. (Also, I lived in Granada, which is famous even in Spain for having incredibly rude people.) Cashiers will unsmilingly fling your purchases at you. Old ladies will push you off the sidewalk. Strangers will shout at each other over the slightest provocation. Spanish people also don’t queue and are big shovers.
However, this isn’t so much rudeness as it is a cultural lack of social obligation to strangers. A Spanish person who gets to know you will be the nicest, friendliest, most hospitable and generous person you’ll ever meet.
Russian(s) is known for being a rather blunt language. In English, you’d say, “Could you please pass the salt?” In Russian, you’d say, “Give me the salt,” optionally adding please. It’s also a non-smiling culture; if you walk down the street with a big grin on your face, people will tend to think you’re crazy or DD. A friend also called it “the land customer service forgot”: Clerks at the market do not smile when they’re ringing up your order or giving you your change. They ring it up, tell you how much it costs, then put the change in the little change dish. You can read that as rude; I found it rather pleasantly blunt and honest. When a Russian clerk smiled at me, I knew it was genuine.
Separate out rude cultures from those that speak a second language rudely. That’s without getting into asking questions that are normal in say China but considered rude in the US (“why aren’t you married yet?”)
Ah yes, New Jersey!!
When I was in Madrid, the local Spaniards were the friendliest, most happy, kindest folks I’ve ever met. Also the locals in Toledo. I mean the well-to-do, the service industry, the farmers, the blue collar types, the shopkeepers, the locals I met in the bars and on the street. Everyone, I think, except maybe the Gypsies; they tended to be kind of rude.
Huh. Sounds a lot like New England 
Yep as a Finnish Australian I love how my Finnish relatives are aloof. They would never leave you to die in the snow but I do appreciate not having to be nice all the bloody time!
Most of my contact with other cultures is when I’m traveling, and am in contact with other tourists. I used to think Americans and Germans were the rudest, until I started seeing more and more Eastern Europeans. I’m appalled at some of the behavior I’ve seen.
But the all-time rudest single individual I’ve encountered was an [del]American[/del] Texan.
This stereotype comes from the veneer of extreme politeness to which guests are treated. In is, in no way, indicative of that society as a whole.
Japanese culture is far more regimented, with a far greater set of acceptable rules and behaviors. Just as “Bless your soul” is code for “Go to hell,” excess politeness can also be a tool to express anger or displeasure without the overt appearance of such.
Japanese society itself is a study in factions and rival groups. Governments, corporations, small companies, social groups and schools are filled with rival groups and constant power struggles.
On a basic human level, humans are creatures of both conflict and friendship. A paradox of good and bad. While it shows and extreme, watch the baptism scene from Godfather, and edit it into two entirely different movies.
I’m not comparing Japanese society as a whole to the mafia, but rather look pointing out that a simplistic view does not stand up to careful scrutiny.
Go around Asia and you’ll agree it’s the Koreans. From taxi drivers to ticket booth ladies to sales ladies. Ever had a sales lady in a dept store say to your face just before turning round: “I’m busy!”
Those folks were probably ultra-orthodox Jews, possibly Hasidic. So you are correct in calling them a “subset.”
(Now I’m imagining a little Chinese guy with a black hat and peyes saying “That shirt ugly. Can I have it?”)