There do still seem to be some vestiges of the post war anti-Americanism, both in the UK and even here in Europe. ("Overpaid, over-sexed and over here"). For many, their only experience was with the GIs, who were young and inexperienced and only here for the beer, not at all interested in where they were (there were anecdotal tales that some of them couldn't even point out on a map where they were posted.)
I have not found this to be the case and have often met Americans who know more than the locals about local history/culture. Or they have taught themselves some other specialist subject and are extremely knowledgable and a joy to talk to.
As has already been said, there are lots of them back home, though. Some are nice, some are not, just like anywhere else. I'm certainly doing my bit to stand up for them if needed, as I grew up with an extremely bigoted father who was anti-everything except Germans and Scots, and towards the end of his life he even started to turn against the Scots!
His attitude was so ridiculously extreme that it made it clear to my sister and me that it was really stupid to make generalisations and denegrate an entire nation or other random group of people.