How do you deal with cultural clashes?

I had just seated for lunch this afternoon, alone, when a couple of guys sat down at my table across from me. They finished their meal and were getting up to leave when one of them turned and said (paraphrasing):“Hey, you know what, you need to get some manners. When you kick someone under the table, you should have the courtesy to apologise.”The actual version was much longer. I was naturally flabbergasted. The best I could muster up was “sorry, I didn’t realise it was your leg.” It left me upset for a while. This person had the concern to tell me I was doing something wrong. How often was I being insensitive to the people around me, leaving them upset and silent?And then it occurred that this was the same smartass who sat at my table without bothering to ask if I minded, or if I was expecting someone, and then talked loudly throughout the period, so much so that when he addressed me it was a couple of seconds before I noticed.The world is full of self-righteous people.With the clarity of the hours that have passed since, I think now this is a classic example of a cultural clash. In my culture, an accidental bump is best ignored because it wasn’t intentional and doesn’t deserve the attention. (I most certainly didn’t kick him; at worst, our shoes brushed.) In his culture, it is acceptable to hijack someone’s table and later give them a lecture on manners.How do you deal with such incidents? Especially those of you living far from home? Do you silently ingest it as a lesson in local culture, or do you snap back at the smartass and make a case for why he should be as accommodating as you were? What would you do?That asked, if I see the guy again, I intend to give him a piece of my mind.