I once told someone that people of my ethnic group are rude and don't bathe.
I said "Haven't you been to (Ancestral country)?
He had to agree with me.
One of your observations is a hard fact (how habitually people bathe).
The second (people are rude) is not. I won't go into the American culture/cultures debate, but you made it clear that you are talking about a different country. Etiquette is not is not a single, global standard - each culture has its own. Some are more similar, other more different.
If you think an entire culture is rude, perhaps you are measuring them by the wrong standard. They may do thing that to your culture is rude, but not to them.
A trivial example: in my country, TY notes are unheard of (and the concept would be considered ridiculous). Why? Because, for us, thankfulness is expressed in person and not by a note, which would seem cold and snobbish, specially if written only because "etiquette says you have to".
At the same time, Americans seem rude to us, as they will often engage in "hostile" eye contact (from our point of view) and are often too brisk to be "nice" and "attentive".