If you're on your way to Paris, be warned that the Parisians treat everybody like shit, including each other. While they will be certain to toss in "Amaricain" every once in a while, don't sweat it. They have to toss in something. If you were German they'd toss in "bosch" or "schleu" (however it's spelled).
The upside is that you may act equally rudely in return, and everything is OK; in fact, they kind of expect it. Not doing so is a sign of weakness. Just don't criticize them for being French, but for being Parisian. Bringing up the WWII thing will get you nowhere, you'll sound just like the Griswolds. They have only heard it about 1000 times, and true or not, it's really lost any force over there.
Go buy a little book called "Nasty French" or something like it. It has shitloads of disparaging phrases that make learning French fun, and that will defuse a nasty situation a lot of times.
And, don't forget that once you learn to act as they expect people to, they can be seriously decent people. One time I was at the Louvre, witing to get a picture of a couple of Rodins. Everytime the shot was *almost* clear, some tourists would blunder in and ruin my shot. After about 10 minutes of my waiting politely, a security guard came up and asked my if I needed help. I said yes and he cleared everybody out right then for as long as I needed to take about 5 shots. I was dressed like shit, and looked about 150% American, so he knew I was a tourist. The deal was that I was polite, I didn't shove my way around, and I spoke some French, and that's all it takes.
I cannot stress enough that you need to learn as much French as you can. Since you will never be able to learn enough to satisfy the French, hell, even they can't, and they know that, whatever you have will do so long as they think that you are trying.
How are you going to Italy? If you're driving, it's about 10 hrs to the Italian border driving straight through. The farther south you get, the more they like Americans, BTW.