The president of a democratic country is a reflection of its people's intelligence and the state they’re in. Honestly, I can’t believe the majority actually buy into this false bravado clown show.
Now, if you slap a '100% tariff' on a majority of the global population, covering 43% of the world’s GDP, major shares of critical resources, and the primary driver of current global GDP growth (which, by the way, is over 10% higher than the entire G7 combined), you're basically asking for an economic collapse. And not a slow one, either.
On top of that, if these countries decided to ditch the dollar altogether, your tariffs wouldn’t even matter. They wouldn’t be selling to the US in the first place anymore themselves, so why would they care about your tariffs in that scenario? At that point, you can only attack them militarily.
At the end of the day, the dollar is just a middleman currency used for trade between nations, it’s not valuable because people want and can get some 'American goods' for example. Take away its role as a trade intermediary currency, and it becomes completely worthless in an instant, and the US collapses as an export market for goods.
Also, someone should probably let him know that they've already been de-dollarizing parts of their trade (and more stuff) for years, switching to local currencies. And if a joint currency doesn’t happen, it won’t be because he said so, it’s just unrealistic logistically plus conflicting interests.