Consider observing someone getting a taste of their own medicine, reaping the whirlwind or whose chickens are coming home to roost.
In some ignoble, jealous way such situations can be satisfying for observers, particularly if they were, themselves, hurt by the previous state of affairs. Is there a specific term for this hollow laugh of an emotion in an observer?
There may well be a certain cosmic irony to the situation, it might even exemplify vengeance. It exemplifies schadenfreude and, as such, is a lot less noble than the satisfaction of seeing justice done but is, presumably, conveniently mistaken for it.
But none of these seem to be on the button for what seems to be a very common emotional state. Many very precise words for other characteristic emotional states exist in various languages (sehnsucht, hiraeth, schadenfreude, saudade): a loan-word would also be interesting to hear, but this also gives me hope that such a word may exist in English.
Words would be more interesting than phrases, but both will do. (It is, after all, idea easily expressed by description).
Sample sentence: I watched aghast, disgusted and, I admit, with certain a certain sense of X, as the tyrant's great machine -- terror of Megalopolis -- turned, to pin its lifeless, limpid eye upon its own inventor.