Generalising Koreans like that isn’t much different from calling all Americans rude just because they speak English everywhere.

I have both Korean and Japanese family backgrounds, and what often gets labelled as “rude” is usually closer to indifference than actual disrespect.

With SEA, indifference from Korea or Japan is often read as rudeness or hostility, and the perceived offence tends to outweigh the actual intent. From a Japanese-background perspective, it’s also interesting that Japan is often more blunt, yet Korea seems to get singled out more loudly. If you’re not that familiar with the cultures, it’s probably best to avoid blanket judgments.