There's nearly nowhere you could fire a warning shot upwards without striking one of the many things that pollute the dome's skies, which would need to elicit an action. Even if you stray away from the traditional straight up in the air warning shot, you can't fire anywhere on level with where you're standing without striking one or more of the ambient population, and shooting a bullet into the ground starts to defeat the point of this intimidation tactic where you're trying to look rad with a gun.
Really, if you're aggressing someone with a gun and you're not actually planning to shoot them with it, just the act of pointing a gun at someone should be enough. Shooting a bullet in the air harmlessly proves your intent no more than pointing the gun at someone was already doing.
It might be funny to fire in the air and elicit some message in the room about a flying object veering downward and crashing, but I don't know how difficult it would be to create what amounts to a new verb that doesn't target anything, drains one bullet from a clip, and causes one of a number of messages that would have to be written from scratch.
For corpses though, I'm pretty down with the idea of being able to attack a corpse with any weapon and elicit real awful messaging, though this idea of 'ruining' a corpse might run counter to a desire to ensure the various death timers aren't something other players can alter with such a simple action.