Boy, have I been "Yank Bashed"!
My Ex is from England and I was attracted to him partially because of that and because I was a "Britphile" since I was a teen after Monty Python, Benny Hill and all the British Sitcoms hit the US.
Shortly after we started dating, he started the "that's not the proper spelling, that's not the proper word, that's not the proper phrase" shit with me and I constantly resisted him saying what you all are saying above: American English is a different beast than British English and since we were in the US and he chose to live here, wouldn't it be easier and more productive if HE learned OUR way of speaking, rather than trying to convert the entire US population over to HIS way? When in Rome...Do As The Romans Do, Right? He didn't like when I said things like that. In addition, I had a somewhat pronounced Philadelphia accent at that point and pronounced things a bit differently - especially when I was around my family.
When we went to visit his family in England later that year, I felt very insecure about myself and my nationality because of this constant battle between us. Also, I had never been overseas before and in addition to not knowing how things worked at Customs etc. (he just left me at the Customs line saying, "I'll meet you at Baggage Claim") I was afraid to speak to anyone thinking they'd hear that I wasn't English and they'd criticize the way I spoke just like he did all the time.
We were in London before visiting his family in Sudbury, Suffolk, he finally said to me, after I asked him to ask someone for something for the 1,700th time, "Is there a reason you're not speaking to anyone???". I told him that back home, he constantly corrected the way I spoke and told me that I spoke like a "commoner". I began to cry right there in the streets. He held me and promised he wouldn't do it again and encouraged me to speak to people to get over my fear.
So, in order to transition into it, I'd put on a fake/bad English accent and ask for my own damn Diet Coke! It wasn't until we were sitting at a show in the West End that a very nice older man interrupted us after overhearing me speaking and said, "Excuse me, but I hear from your accent that you're from The States, is that correct?". I told him I was and he proceeded to ask me about Broadway and Hollywood and we spoke for about 15 minutes and I became a Celebrity and had a lot to offer this man. My fears were gone!
When we got to my Ex's family's house, I had confidence and they all liked me (except his Mother) and they did the same thing - they asked me questions about growing up in the US, about my family, about living in New York City and about other American things. I was the first American that most of them had met, and even though my Ex was living in the US, I was "the real deal" and had a different perspective on it all, not just the perspective of a Brit living in the US there to criticize everything and every one because it's not British, which is what my Ex seemed to do every day.