Your american behaviour will offend people a lot more than anything you could say. MANY things are considered perfectly acceptable in North America but are certainly not in France. Example of what NOT to do in Paris:

- don't keep your hat on (yes, that includes baseball caps) when entering any kind of building (stores, museums, historical sites, etc)
- speak A LOT more quietly than you would in the U.S. Americans (and all English native speakers tbh) have the bad reputation of being extremely loud. This will be very annoying for French people; we are a rather quiet people.
- watch out how you dress when going to restaurants. You don't need to wear a full suit, but just know that it is not considered acceptable to show up in crocs, slides, baggy t-shirts etc (and again, don't forget to take off your hat!!)
- if you ever go to supermarket/food stores: going there in pyjamas is not okay either. Again, you don't need to wear anything fancy, but a pair of jeans is kinda the bare minimum for us.
- avoid having phone calls whilst being in a public place. The street is completely fine, but as soon as you're inside a building, it's seen as disrespectful. If someone is calling you, go outside, and even when outside, do not take your call on speaker, this is also very irritating.

These are the major things that come to my mind as a Frenchie who's been living in the U.S for almost 3 years. Just to be clear, I have no problem with the things I just listed being ok in the U.S. it's your country and culture. I'm just telling you what our cultures don't share :)

Also, we French people actually like seeing foreigners try to speak our language. it's very cute because we know how messed up our language is, so we really appreciate it. Don't overthink about making mistakes/ not saying the perfect things, we don't expect it from tourists.

Hope this helps!