I personally think ALL of his Canada BS is mental, so, no arguments there. But what right does Mexico have to object to what we call a body of water? He's not renaming what we'll call Mexico itself.
These things serve a real purpose which is to troll the easily offended. In that, it's a huge success, as every breath wasted whingeing about this harmless renaming is one that isn't used to ask good questions like "Why fight a trade war with Canada instead of asking why we even have free trade with a country (Mexico) whose wages are so low that it promotes the gutting of American industry." That would be a good question to ask Trump.
We should have a bilateral trade deal with Canada, which would strengthen both countries, and cut Mexico out of it. But all this has distracted from how poorly he's executing his tariff strategy.