Characters
I suppose you think that was terribly clever.
— Gandalf ‧ The Lord of the Rings: The Fellowship of the Ring
Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The speaker responds to someone's move with dry, irritated sarcasm, supposing that the person is pleased with their own cleverness. The word terribly, used with pretended admiration, sharpens the reproach and suggests the speaker is unimpressed, though the words alone do not show how serious the annoyance is.
Context reviewed