Stuck for an answer

How rude can I be despite/in spite of my supposed poshness? I was invited to a dinner party last week and the hostess put out place cards with our names written on, even though there were only seven of us there. Two days after the party, I received in the post an 'At home' invitation card - obviously, it was late and also, it was a bit much for just a small supper party. These things are a bit non-U but she was American, so I think the rules are different. They are vastly more mannered and polite across the pond. Plus I was rude to her brother and had to apologise the next day. So I think, frankly, had she served up toe jam and asked us to hold hands and sing hymns before the starter, I'd have to concede that her manners were better than mine.

In this instance - was I posh, or not?