On the face of it Poirot's glance conveyed humorous impatience.

Answer: Option C

Humorous : causing laughter and amusement; comic.
Disappointed : sad or displeased because someone or something has failed to fulfil one's hopes or expectations.
Dejected : sad and depressed; dispirited.
Pathetic : arousing pity, especially through vulnerability or sadness.
Dismayed : cause (someone) to feel concern and distress.

Antonym of Humorous is Pathetic