Forget nicknames, how would these people feel if somebody just said "Hey I'm going to call you Arnold now, because you fit my mental image of Arnold." Wildly inappropriate thing to do?

If you want to go and impose whatever pronoun you want on someone based on how they look, don't act shocked when you get called out for being a dick to them.

I've not seen someone suffer negative consequences for calling someone else the wrong real name. I've seen instances of negative consequences for someone using the wrong pronoun though.

Or is it because deliberately going out of your way to call people the wrong name to make a political point isn't a thing that anyone does, so nobody has needed a rule to make them knock it off?

You know, in being subtle like that, I fear you might not be making your point clearly enough for the others.