I was born and raised in the UK, and just returned to the UK after ten years in the States. I have been quite surprised by how many people assume that it is OK to share all their various mistaken assumptions about America and Americans (everyone is so fat over there, people just drive everywhere, the food is awful, everyone's super-religious and gut-toting, etc.)
Has anyone else encountered this phenomenon? I tend to use those moments to set people straight or at least complexify their worldview a bit, but it really bugs me that people just assume that I'll laugh along with them at all those 'stupid Americans'...