Does the fact that I didn't know about "tipping culture" when I was first time in the US makes me an asshole?
If you are in the US and received good service, but left crappy or zero tips then yes, you definitely leave a negative impression of yourself. Nobody will understand why you left a bad tip or just think "oh, he's a foreigner, he doesn't understand." They will just think you stiffed them. Or they will perhaps think - "oh he's from country X - they must all be cheap assholes there. I hope I don't get any more tables with people from that country."
Would it not be the same if I visited your country and was rude or insulting regarding some very basic and obvious part of your culture?
People may differ about what is "obvious." Something that doesn't exist in my country and that I've never heard of ... is not going to be "obvious" to me.
Bullet point #1. I would consider that fairly obvious.
If you can't manage to stumble across #1 cultural tip then you obviously have not done much research. You shouldn't expect people to excuse your ignorance of their culture. That goes for any country - not just the US.
This is generally what happens. I have a few friends who are bartenders/servers and they loathe Australians.
But to the average Australian - we have a very decent minimum wage and ridiculously good penalty rates (like, work a public holiday and you get double time or double time and a half). Tipping is just something that is non-existent, and I think people just don't expect that the US would treat people so much worse than we do...
[1] I've lived in the USA almost my entire life, and have never understood why "we" are "Americans" when there are many, many other countries on both American continents that aren't "Americans". Why is there not a term for us that is more accurate and less Americentric (wait, really?).
The country is called "The United States of America," so its people are "Americans." Similarly, people from "The United States of Mexico" (yes, that's its real full name) are called "Mexicans."
Languages evolve as an emergent property of people who speak them. Language usage is not subject to revision or control by self-appointed intellectual fairness monitors who unilaterally arrogate to themselves such an authority. Linguists call this practice "prescriptivism," and it is widely denigrated as (ironically) an imperialist tactic used by the power class to enforce their social position.
However, the principle itself is not limited to any particular political orientation; leftist prescriptivism is just as unsupportable in a linguistic sense as imperialist prescriptivism is.
You might see on many left-wing president's speeches, they start with "Hermanos Americanos" ("American Brothers"), which definitely does NOT include the USA :P .
I'm not a prick so I'd shrug it off as someone being ignorant of the local customs.
He was from the US, and I don't think he was being an ass-hole.
Basically restaurants are the only place where tips are absolutely expected and you can make yourself look bad by not tipping. For anything else, if I'm not sure I usually just check a travel guide or go on forums and ask other people what they do.
I would do this if I travel to any country, just ask around at how you should behave if you want to fit in.
You even admit that locals barely know what's expected in some situations!