The men in the narrator's platoon are on relatively light duty as they are stationed away from most of the fighting for now. In chapter eight of Tim O'Brien's The Things They Carried, the narrator mourns the loss of fellow soldier Curt Lemon by telling this story about him.
The Army sends a dentist to O'Brien and his fellow soldiers as they are putting in their time in this resort-like setting near the beach, and the dentist is neither an impressive nor an intimidating man. He sets up his field tent as his office of operations.
He was a tall, skinny young captain with bad breath. For a half hour he lectured us on oral hygiene, demonstrating the proper flossing and brushing techniques, then afterward he opened up shop in a small field tent and we all took turns going in for personal exams. At best it was a very primitive setup. There was a battery-powered drill, a canvas cot, a bucket of sea water for rinsing, a metal suitcase full of the various instruments. It amounted to assembly-line dentistry, quick and impersonal, and the young captain's main concern seemed to be the clock.
It is clear that there is nothing about this dentist to inspire fear in anyone, yet Curt Lemon is afraid. As the men sit and wait for their turn, he insists that there is nothing which will get him to enter the dentist's tent. He will simply refuse to go.
When his name is called, however, Curt Lemon does go into the tent--and promptly faints.
It was over fast. He fainted even before the man touched him.
Later, when he comes to, Curt Lemon is ashamed and embarrassed and thinks he has something to prove. Late that night he goes to the dentist's tent, wakes the man up, and then insists that the dentist pull one of his teeth. Of course there is nothing wrong with the tooth, but that is part of the irony. He feels the need to prove his bravery by getting a tooth pulled; what he does on the battlefield, apparently, does not count as bravery.
This harmless dentist inspires more fear in Curt Lemon than being in battle; the thought of letting anyone touch his teeth is more intimidating to him than being on the front lines of battle. What is inside the tent is innocuous, yet Curt Lemon is deathly afraid of it; what faces him on the battlefield is deadly, yet Curt Lemon is fearless there. That is irony.