It will make the trust list system kinda less important. When people trust/distrust others for small reasons, it just decreases the value of trust/distrust. He is not going to be a DT anytime soon. He did not leave any feedback. So adding him to the distrust list does not make any changes. Adding him ignore list is a much batter decision.
I think of it as a preemptive strike, and a bit of lazy.
If they do start tagging and perhaps they do somehow get some people adding them to their trust list it might become and issue.
So, since it seems they are on some sort of bizarre vendetta, give them the ~ and add to ignore and you don't have to worry about it later.
Perhaps not the best attitude, but if they do turn out to be a useful member it's simple to remove the ~
If they create a mess, then other people may have issues that they did not need to have.
Just my view.
-Dave