While it's true I am that variety of grumpy old man who believes that certain elements of inherited grammar and usage should be preserved, this bothers me more than a dangling participle or split infinitive. On reflection, I realized that the use of ‘stealth’ as a verb exemplifies a contemporary trend in table-top gaming that I personally view as an impoverishment of the RPG experience: the replacement of problem-solving by players with simple skill rolls.
When a player tells the GM “I stealth,” they typically then make a roll that tells everyone how well the character succeeds in ‘stealthing,’ and the game proceeds. What is lost in this exchange is the player's engagement with the fictional space. No one at the table is thinking about the details of what is involved in ‘stealthing’ into the room - keeping to the shadows between torch sconces, waiting until the guard's back is turned before silently darting to the next shadowed area, crawling under a table, or whatever makes sense in the fictional circumstances. In extreme cases this lack of thought about the details of the fiction can even lead to absurdities such as PCs ‘stealthing’ across an empty well-lit room in full view of enemies, merely because they rolled a high number on their stealth check.
Of course it is entirely possible to combine player engagement with the fiction and stealth rolls; but when a player describes their attempt at a stealthy act or movement simply by saying “I stealth,” they are forgoing that engagement and replacing it with a die roll. If that is how everyone at the table wants to play then I obviously can't argue with it, but I wonder if the culture of “I stealth” might be giving some new players an impoverished idea of what the game can be. Personally, I prefer a game where dice are rolled only after all the details of a player's action in the fictional space are considered. Replacing all sneaky movements with a blanket “I stealth” roll seems to me a step on the path to replacing an entire adventure with a series of dice rolls - roll for treasure, roll for casualties, the end.
Sean McCoy, one of the authors of Mothership, explains that he did not include a stealth mechanic in the game because he wanted players to engage with the fictional space when trying to hide and sneak around:
The full thread is here; also listen to his fantastic interview on the Mud & Blood podcast episode 71.
In conclusion, ‘stealth’ is not a verb, but if you want to use it that way, you might think about what you are losing from your game when you do so.