So, it’s perfectly legal to plaster bumper stickers all across the back of your car that say “Fuck you!!!” in bold letters. Covering the entire trunk and rear-facing portions of your vehicle. In such position as to be unavoidable to the drivers behind you in traffic. Unavoidable to anyone regardless of their age, gender or religious views. Unavoidable to anyone who isn’t blind.
It is perfectly legal. I know. I checked. In fact, it’s not just the rear portion of your vehicle. It’s anywhere on your vehicle, as long as it doesn’t obstruct your view or violate vehicle safety regulations.
However, you cannot say the F-word on TV, on the radio, in a newspaper, or a newstand magazine (unless it’s labeled for sale only to adults). And we’re all just fine with that. It is as it should be, according to the views of most Americans. Otherwise, they would have lobbeyed their congressmen and senators to change that.