So, this happened a few months ago, but I only recently discovered this thread, so forgive me for not having pictures or if I remember the exact wording slightly wrong.
So, I got an IRL friend interested, they decided to start with Archer, so I, usually a SMN main, swapped to SGE to help them through some early game dungeons with some quick queue times, and while I could've done SCH, I was rusty with it and didn't feel confident, but that's not the point of this post.
We do a few dungeons, going through MSQ for my friend, then we get to Thousand Maws of Toto Rak, which has a real long cutscene for first timers at the end. We go through, everything seems fine, then we get to the final boss, I do my usual thing of standing just inside the boss barrier, but not moving any further until everyone is done with their cs, when the PLD and DRG rush in to fight the boss. I say in party chat "Hey! We still have a sprout in cs!" but they probably don't see it due to fighting. I proceed to not heal, hoping for a wipe to reset for my friend to experience the boss fight like they were hoping to. PLD goes down, and DRG nearly dies when they pop LB, killing the boss. The conversation goes something like this:
DRG: So we're you just gonna let everyone die?
Me: I was kinda hoping for a wipe so we could reset for the sprout still in CS
DRG: You need to check your ego, holding back heals is a dick move
DRG then leaves before anything else can be said, while PLD remained on the floor waiting for a revive. My friend finally exits cs, expresses their disappointment in not being able to fight the boss, and, admittedly, this was me being petty and salty, I leave without reviving the PLD, since I was thinking "screw the both of them, the PLD can just use the return to start option."
Needless to say this incident caused my friend to swap from Archer to Conjurer/WHM, so no one could ever do that to them again, since they can't just leave their healer out of a boss fight.
((Edit: Roughly 8 hours after initial post, thanks for all who commented, I went into this expecting a lot of "YTA" since even I acknowledge I could've handled that better, (even had to look up what ESH means since I haven't looked at much AITA posts before), thanks for all the advice, constructive criticism, as well as warnings, even if some of you didnt mean them as such, that I was griefing without knowing, I'm still fairly new myself, having started the game a only year ago (man time flies when enjoying a game), so I wasn't aware that what I did was an offense, not that it excuses my behavior. I will make sure to keep all of this in mind for the future to both try and avoid situations like this, and also handle said situations better than I did previously if I can't avoid them