Wow, I'm surprised at how quiet everyone is ... I would have expected a load of discussion by now. I apologise in advance if I offend anyone, but I won't be sorry: these are simply personal opinion,s and last time checked opinions didn't bite, and (like all opinions) they are open to being changed. That is after all the purpose of discussion/discourse.
Safety Tools and Mental Health
Here are couple of observations:
1) Self confessed grognards, like the OP, remember a time when safety tools weren't probably necessary. Back in the olden days fellow gamers tended to also be personal friends. Given this people, in any given group, were already aware of each others limits and personal issues without it having to be made explicit.
That's not to say adolescents couldn't be dicks to each other - because that's what growing up and learning to be an adult entails (ie: learning social cues by trial and error) - and dickish behaviour between groups of friends is going to happen at some point and in some form regardless of the presence or absence of a shared TTRPG.
What I'm saying is that adolescent gaming horror stories aren't endemic to gaming - they are endemic to adolescence and just happen, in a given instance, to have involved gaming. If not gaming then it would have been something else.
But now we live in new type of gaming landscape and the hobby has to adapt to survive
2) Personally I always had reservations about the 'x-card' for precisely those reasons given on the show. It seems like a good idea - the problem is not all good ideas are actually good ideas. There a reason the mental health profession takes a long time to validate 'new' treatments - the law of unintended consequence.
The x-card, and similar, are victims of this law. Again, it's a good idea that simply wasn't thought thru before everyone jumped on board. The other truism of any social science also comes to mind - The road to Hell is paved with Good Intentions.
Listening to the OP's experience, with trying to be as accommodating as humanly possible, another thought struck me: weaponised insecurity. Public 'triggers' can be abused on two different levels. The first is can it just become another tool in the arsehole players arsenal to beat the game and 'win at DnD'; eg: don't like the way an encounter is turning out, hit the x-card and force the GM to reset their narrative (bit like save game, die, reload in a computer game). -
The second level is bit more complicated, but a very common occurrence in mental health - manipulation. People can use it shift the focus onto them ('look at me, don't look at me'). At that point you are in delicate territory, sometimes the manipulation is a defence mechanism sometimes it is more complicated. To be honest I could easily write 2000 words about the different forms and reasons why - and it would be a very dry and boring read. So, I'll use a comic reference that, though it over simplifies what I'm getting at, should give the average person an idea of what I'm saying - imagine The Joker playing DnD with his fellow inmates at Arkham and the DM is Dr Quinn.
I believe, in this new world of online gaming, each and everyone of us should be careful and exercise the same caution/precautions we use with our social media accounts (I assume most Jackers are intelligent and, therefore, sensible with their social media)
3) I agree that sometimes you cannot win. The OP has done more than enough in trying to prevent problems before they arise. The player that (ironically?) messaged about their inability to message due to anxiety? here's a word of advice: some people just want to make you feel bad. Because in making you feel bad they get validation in gaining (what they feel) is a degree of control over you. ie: "I'm just texting you to say I get anxiety when I have to text, look at what you've done to me, you should feel ashamed of yourself".
Now, I know, narcissism (as in the personality disorder) is trending high in the internet zeitgeist of late - and nearly everyone who does something we don't like gets this label - doesn't mean that there aren't narcissists out there. I vastly suspect that, given the OP's description of events from game to after game discussion, that this might be one of those times when it rings true. As said, going from laughing at dick jokes in game etc to 'you should know I get anxiety when I have to text' strikes me as indicating the possibility that that is what you are dealing with: because the narcissist craves exclusive attention and it's never their fault. It's less about how you accommodate them but more about the fact that you must accommodate them and the effort required to accommodate them is more important than the actual result of your accommodation ie: every time you solve a problem, they'll shift the goal posts.
What do you do? guess you have to be a bit selfish sometimes, if you know you have have done everything reasonable, and you still can't 'win' then cut and run. Remember rule 2 of GMing - if it stops being fun for you then stop.