Antiphrasis
Saying the opposite of what you mean while letting the true meaning show: "Great job!" facing a disaster.
Antiphrasis states the opposite of what it means to convey: "lovely weather!" under the storm, "smart move!" after a blunder. It's irony's elementary mechanism — the true meaning is written nowhere; the reader reconstructs it from context.
Everything therefore rests on signals: exaggeration, obvious gap between statement and situation, punctuation. Too discreet, antiphrasis gets taken literally (written irony's classic risk); too heavy, it loses its elegance. In dialogue it characterizes power dynamics beautifully — who is allowed to be ironic with whom maps an entire hierarchy.
Example
"Well, that went brilliantly!" (as the project collapses).