One of my friends is really phobic of >thing<. We discovered this when >thing< occured in the plot and he freaked out. I'm not sure the DM quite realised how much of a problem it was, as >thing< has now come up twice more, quite possibly to provoke a reaction from the player.
The player doesn't want to make a big thing of it, but it's pretty obvious to a few of the players at least that it is a genuine issue. Is it the player's responsibilty to tell the DM to back off or can someone else jump in?
It's a fairly common trigger, but I'm not sure I hold with trigger warnings for everything on the off chance... but now it's come up, how best to deal with it?