> carries no informational content other than "fuck you".
If that's your argument, you should know that saying "fuck you" in the US is, broadly speaking, a protected free speech right. Including for childish, offensive and information-free reasons. This means there is plenty of case history to test your analogy.
It is a protected free speech right, for example, to say "fuck you" to the cops - https://www.vice.com/en/article/wxdbqz/saying-fuck-the-polic... .
It is a protected free speech right to post a sign in your yard saying "Fuck Biden and fuck you for voting for him", even if that's childish, offensive, carries no informational content, and shits on 81 million people. https://freespeechproject.georgetown.edu/tracker-entries/jud... (sign at https://www.thefire.org/sites/default/files/styles/860x484/p... )
You can read more about how "fuck" fits into the US concept of free speech at https://en.wikipedia.org/wiki/Cohen_v._California with Cohen v. California (wearing a jacket saying "Fuck the Draft" in a courthouse was free speech) and its followup cases. In particular note how Blackmun, in dissent, said wearing the jacket 'was not speech but conduct (an "absurd and immature antic")'.
So if that's your argument, you've already lost ... in the US.
Denmark, of course, is another country.
> it's almost rude to not put your pronouns in email signature
Wow! I don't know what sort of people you associate with, but almost none of my email signatures have that. I just checked - four distinct people over the last year, all from a librarian list I'm on.