"Two cultures separated by the same language"

I keep finding myself amused at a little incident that happened during our visit with Kev and Geraldine:

While we were in Savannah people-watching, Geraldine noticed a man begin to get unpleasant with another man. Then the unpleasant man headed in our direction and Geraldine made sure Kev was aware of him. He passed us by without incident, but Geraldine exclaimed that he was 'getting shirty' with that other man. I leaned toward Kev and said "Shirty?" (asking for an American equivalent of the British colloquialism). Kev responded "Stroppy." Hmmm.

The look on my face must have communicated my confusion, because Kev immediately followed with 'arrogant.' OK, now I get it. I need to get out more!