In response to the previous post, you might want to talk to the people of Normandy or many other places that had so many friends and relatives killed by the Allied troops. They certainly don't look back on the invasion as a good thing. They certainly weren't excited about being a part of the Nazi nation but they hadn't suffered the destruction of their homes and their region until the Allies invaded. There are plenty of other folks in Europe that didn't feel that getting bombed into the stone age and suffering from famine and disease and the loss of their sons and husbands and fathers to the Allies was necessarily a happy thing.
I think for the most part the relationship between American GI's and the European civilians was a good one. As someone else has mentioned for many we were seen as liberators or protectors. As in any case though, I am sure there were instances of not so good relationships.
Absolutely. There were also many instances of genuine friendship and good will too, but in any conflict, and certainly in one so horrible and bloody as World War II, not all American soldiers treated civilians well. After the friends they had lost, the wounds they had suffered and the horrible things they had seen in war, many of them felt angry and bitter towards a German population they felt had supported Hitler, even if that were not the case. I do believe that ill treatment towards civilians was the exception rather than the rule, which was not true of the Red Army and their entry into Berlin.
Of course, there were surely instances of bad blood since there will be instances any time that many people are put somewhere. However, the relationship between American soldiers and European civilians was basically good.
The place where there was the most tension was in England. You will run across, if you read enough about this period, the complaint by the British that the Americans were "over paid, over sexed, and over here." This clearly reveals the sources of tensions -- many young men, relatively wealthy compared to the war time British, competing for women and just generally causing change.
In places where the Americans came as liberators (say in Italy or France) things were different. I have heard nothing about any widespread ill will in those areas. I should emphasize that there were no major incidents, though, even between British and Americans.