I lived in England this past summer for 2 months. I have nothing but positive things to say about my experience and all of the English people that I met. I was never treated with disrespect or negatively because I was from the US.
I do find that many Americans, when abroad, act like spoiled brats because things aren't the same as they are in the US. Hello! That's why you travel - to experience new things... There were numerous occasions when I was quited tempted to burn my passport and renounce my citizenship because of boorish American behavior. Moral of the story - if you act like an ass, regardless what country you're from, people won't like you.
I am probably more anti-american now than I was before, but I really had a lovely time there and can't wait to go back. It's a great country.
Service in restaurants does tend to be slower than we are used to, but just chalk it up to cultural differences. Buy someone a pint, and you have a friend for life
.