Nausea Dissonance

A character either witnessing a nauseating sight, or describing something nauseating, is completely unbothered by it. Bonus points if it makes another character nauseated. Frequently Played for Laughs.

Often leads to a Vomit Discretion Shot or Vomit Indiscretion Shot.

Comic Books

In the Warren Ellis comic Fell, the coroner presents a rotten corpse to Detective Fell while eating a sandwich. After taking a bite, a piece of tomato falls into corpse's chest cavity. The coroner reaches in.

Fell: If you retrieve that piece of tomato from where it fell and then put it in your mouth I will shoot you.
Coroner: ...I was simply going to remove it. I have to go over the bridge for organic tomato, you know.

He eats the tomato anyway.

Film

In The Hunt for Red October, Jack Ryan is aboard a very turbulent plane to the USS Enterprise. Jack hates flying due to turbulence, but the navigator goes into excrutiating detail about a past mission:

Navigator: What's the matter Commander? You don't like flying, huh? Aw, this is nothing! You should've been with us five, six months ago! Whoa! You talk about puke! We ran into a hailstorm over the Sea of Japan. Everybody's retching their guts out! The pilot shot his lunch all over the windshield, and I barfed on the radio! Shorted it out completely! And it wasn't that lightweight stuff either, it was that chunky industrial weight puke! (offers him the candy bar he's been eating) Hey, you want a bite?
Jack Ryan: (muttering to self) Jack, next time you get a bright idea, just put it in a memo!

In the Dirty Harry movie Magnum Force, Harry is called to the scene of a murder with his partner. One of the cops there comments on how the inside the victim's car is just filled with all kinds of brain parts (the audience doesn't see this) and generally goes into the most gross bodies he's seen. Harry is unaffected but his partner looks at the body and then turns to go puke.
- Even the first Dirty Harry movie involves Harry telling someone who is considering jumping off a building that he wants the guy's name, because the mess of a splattered body often makes people hard to identify. The guy says he thinks he's gonna puke, and Harry, who doesn't seem nauseated at all, says "don't do that, not with all those people down there looking up."
In National Lampoon's Vacation, after the Griswolds discover their dog had peed on their sandwiches, everyone starts spitting their sandwich out except Grandma Griswold, who just keeps eating.

Live Action TV

In the Married... with Children episode "Hot off the Grill," everyone at Al's cookout reacts with disgust when they learn that Kelly added the ashes of Marcy's dead aunt to Al's grill. Everyone, that is, except Steve, who hated said aunt...and starts grinning as he eats his "Bundy-burger" with even more enthusiasm.
This comes up from time to time on Bones, where Brennan and the other squints at the Jeffersonian are unfazed by decaying corpses and whatnot while other characters get squicked to varying degrees, including having to vomit.
Dirty Jobs has this happen all the time. There was an episode where a cameraman literally stood under a shower of condensed raw sewage and didn't even flinch.
On the American version of The X Factor, the first act of one episode featured a flasher who got on stage just to expose himself to the judges. While 3 of them were totally fine, Paula went to the bathroom to vomit for about 15 minutes.
Kari Byron, of MythBusters fame, would gag and choke at the sight of the pig corpses the team would use for ballistic analogues while the boys were happy to carve and lift it with bare hands. She's gotten better about it, though.
An episode of CSI has Catherine send the rookie officer escorting her out because of this trope (she doesn't want vomit contaminating her crime-scene). The suspect turns out to have been hiding, and attacks her.
- Lampshaded by Warrick in another episode, when Sara admits that she's being nauseated by a boxer's spit bucket. He'd seen her working on decomposing bodies or feces without complaint, but saliva turns out to be her personal Blow Chunks button.

Western Animation

In the King of the Hill episode "My Own Private Rodeo", when Dale recounts how he caught his father, Bug, kissing his wife Nancy on their wedding day, his story starts off catching Bill puking in the bathroom, and afterwards, nonchalantly heading straight to the kitchen, where he caught Bug in the act.
In the Futurama episode "Parasites Lost", after learning there are worms inside Fry's body:

Hermes: (eating popcorn) It's nauseating, mon! (eats more popcorn) Is there no way to get rid of the disgusting maggots?

Happens a lot in Superjail, where disgusting and violent deaths are commonplace.

Real Life

Compulsive hoarders, particularly animal hoarders, are often oblivious to how foul-smelling and unsanitary their homes have become.
Medical personnel build up a resistance pretty quickly. Autopsy Snack Time is, after all, Truth in Television.