Toasted Buns

These jets are burning my ass!

—StarCraft II Reaper unit's Stop Poking Me quote

The Jet Pack is the consummate icon of the early years of science fiction. This device represents the ultimate in convenience and personal mobility. Just strap this back pack sized object on and travel anywhere you'd might want to go. Never mind the actual technological challenges in making such a device practical.

However, the standard depiction of the Jet Pack in media has one problem: The proximity of the jet exhaust to the seat of the pilot's pants. Without some Unobtainium-level heat protection, the pilot's rear, thighs, and possibly calves would get charged to carbon within minutes (or seconds) of firing the thing up. Yet going back through all the rocket man serials of the 1930s and the homages to them, we see no attempt to shield the Jet Pack operator from this simple operational hazard.

This issue is likely ignored for the same reason that no one ever calls anyone on Convection, Schmonvection: If the flames aren't visibly in contact with the pilot (or visible at all in the case of certain combustible gases), then "obviously" there'll be no harm.

See also Farts on Fire and Rump Roast. Not to be confused with the hilarious results of sitting on hot things.

Examples of Toasted Buns include:

Anime and Manga

Chachamaru of Mahou Sensei Negima sprouts a jetpack from her back in this manner. Though she herself is undoubtedly resistant to heat, her standard issue school uniform always remains unsinged (might also be a case of Magic Pants since the jets appear through her blouse and blazer).
Averted in Digimon Savers. Gaomon and Agumon get jetpacks as part of their evolutions to Machgaogamon and Rizegreymon, respectively. The former gets the jet part at the ends of the wings, while the latter has jets as part of the wings (and point away from his tail).

Comic Books

Lampshaded in an early issue of West Coast Avengers, where Wonder Man debuts a new (and hideously ugly) costume, with his trademark jet thrusters moved to his back instead of his hips.

Tigra: Won't that burn your... ah...
Wonder Man: Not if your "Ah" is invulnerable.

In Ex Machina, this is a problem for "The Great Machine" once or twice. But that's why his backup always has fire extinguishers.
Gaston Lagaffe designs a jetpack but Reality Ensues when he tests it, burning up his ass and making him run around screaming in pain. After turning off the fire, Fantasio remarks that while it doesn't do much vertical performance, it does a lot of horizontal performance.

Film

Averted in Transformers: Revenge of The Fallen: The thrusters on Optimus Prime's Powered Armor are outboard of the shoulders. They can also pivot, as Optimus demonstrated when he weaponized the backblast against Megatron.
Commando Cody
- Spoofed in J-Men Forever! when a Gag Dubbed Cody complains that his feet are on fire, along with the many other problems of using an atomic-powered jetpack.
King Of The Rocketmen
The Rocketeer tries to handwave this by suggesting that the alcohol-based fuel will result in a cooler flame (which is true)-- but said fuel will not produce nearly enough energy. Points for trying, though.
- In fact, the Rocketeer is flat out bizarrely inconsistent about this - in one scene, the jets set fire to the set, but in another a sheet is directly exposed to the flames for several seconds without even being singed.
Minority Report, anyone? It gets even more ridiculous when the protagonist is fighting a jetpack-equipped police officer inside an apartment without the (blue-hot) jet exhaust setting anything on fire.
- Though to be fair, the exhaust flame does set a few other things on fire. Which is more realism than you'll generally see in a movie jetpack.
Boba and Jango Fett. Though they are wearing what is likely heat-resistant armor. Averted by other Mandalorians in the EU, who make use of a skirt like Kama, which is made out of flame retardant materials to protect their leges.
Averted in Thunderball, which has a real frickin' jetpack. (Though the sound effect was changed because Reality Is Unrealistic.)

Literature

Subverted in the Marvel novel Codename: Wolverine. SHIELD is testing just such a jetpack, with the SHIELD agents wearing a special heat-resistant bodysuit when using it, though tests are brief so far since the reliability is questionable. Wolverine dons the pack so he and Mystique can make their escape (with him sans suit), and gets to put his healing factor to yet another very painful test.

Live Action TV

Actor Robert Duncan McNeill recounted at a recent^[when?] Con of his time as Tom Paris on Star Trek: Voyager that his rear did catch fire from the jetpack in a "Captain Proton" episode. The on site nurse had him drop trou right there to make sure everything was all right. He claims Tim Russ has photos.
At least approached in Upright Citizens Brigade episode "The Story of the Toad", in which Antoine asks two prostitutes, "Hey... How would you ladies like to make love while wearing a jetpack?" but then cautions, "We can't do it doggy style though, you'll set me on fire."

Roleplaying Games

Deadlands hand waves this trope in its Mad Science source book, "Smith and Robards": every jetpack purchased is shipped with a complimentary pair of asbestos pants.

Tabletop Games

Averted in Warhammer 40,000.
- The Imperial jump packs used by Space Marines and Seraphim are built so that the exhaust is pointed outward at an angle from the body of the flier. Their legs are nowhere near the danger zone. Being clad in Power Armor probably helps too.
- The Tau jetpacks stick out very far behind - and again, battlesuits.
- Stormboy Rokkit Packs stick back and are huge. Also, the Orks are tougher than nails and unlikely to be concerned about "minor" burns, short of actually being set on fire.
- Eldar version (Swooping Hawk Wings) uses anti-gravity.

Video Games

Averted/Subverted in the Kirby games with the Jet power. While it doesn't set Kirby on fire, it will toast everything around him.
Averted in Mega Man. Rush turns into a jet platform as he's built for the purpose of being transportation. 6 and 7 have the thrusters outboard of the shoulders on the Jet and Super armors, respectively. Also, characters with built in flight usually use wings or a rotor system to fly. In the Mega Man X series, flying bosses use wings or leg mounted jets. Even if characters have back mounted jets, those point out from the back, not towards the ground. Being robots that are constructed in a way that they operate fine in snow, underwater and Lethal Lava Land doesn't hurt either.
- Er...not to mention pretty much every character in a Mega Man game is robotic in at least some aspects.
Star Wars: Shadows of the Empire: once you reach the Gall Spaceport, you can find a Jetpack with the exhaust directly over Dash Rendar's butt.
City of Heroes has plenty of jetpacks. Some follow this trope, others avert it by having the jets spaced away from the body.
Possibly averted in most of the Duke Nukem games, where Duke's jetpack doesn't appear to blast anything dangerous out of the bottom.
- From the noise and lack of flame, it would appear Duke's jetpack is more of a ducted-fan type of thing rather than any sort of combustion engine.
Kingdom of Loathing. Lampshade Hanging in the item description for the toy jet pack:

"It's of the "concentric rings of energy" build rather than the "gouts of flame" build, so at least it won't singe your butt when you go flying."

Averted, though perhaps partially used in the game Cortex Command. Soldiers with jetpacks have the exhaust come out just below their butt, which might normally singe their legs. But, they automatically bring their legs forward when jetting so their legs won't be burned off. There are two downsides: first, if you try to use the jetpack while landing, the solider might fall on its torso rather than feet, resulting in more damage, so the last second before touchdown needs to be jet-less. Second, the game's designers haven't yet made a separate "kneel" animation, so when you try to kneel, the soldier puts his legs in front of him like he's just waking up from bed, and it looks silly.
Averted in the game Soldat, since you have rocket shoes rather than a jetpack.
Also averted with The Fury's jetpacks in Metal Gear Solid 3: Snake Eater, in which the boosters are outboard on his shoulders. One thing to note: it's rocket-fuel powered. By the way, his flamethrower also uses rocket fuel.
Averted in Outwars; the jetpacks have the nozzles rotated by 45 degrees so that they can't possibly hurt the operator. The way this is depicted is not perfectly logical, as such an orientation would waste half the power of the pack attempting to move the operator horizontally against itself, but it's still better than having your lower half vaporized...
~~Subverted~~Weaponized in Tatsunoko vs. Capcom, where about a third of the PTX-40A's normal attacks involve roasting his opponents with his thruster-fire.
In Halo, some of the brutes have jetpacks, but the exhaust ports are around the shoulders.
In World of Warcraft, for the airship battle event in Icecrown Citadel, players may equip themselves with jetpacks that allow flight to the opposing faction's airship. These jetpacks appear to operate in the traditional "toast your buns" fashion, and even get their lack of safety lampshaded by the dialog of the player accepting them. But what's particularly hilarious is that Druids can equip them while shapeshifted into Dire Bear form, resulting in a bear with a jetpack literally strapped to its butt.
- ROCKET BARE! BURNIN' OUT HIS FUSE OUT HERE ALONE!
In the videogame adaptation of the James Bond film From Russia with Love, jetpacks can literally solve all your problems - they're equipped with missiles, can hover on the spot, are easier to maneuver that actually walking - and are readily accessible at many points in the game. Nobody wears flame-retardant armour in the game.
Averted in Grand Theft Auto: San Andreas by a simple use of actual design of Bell Rocket Belt that has exhaust pipes moved away and to the side of pilot's body.

Western Animation

My Life as a Teenage Robot, though Jenny's robotic body might just be heat-resistant.
Dastardly and Muttley in Their Flying Machines, episode "Plane Talk".
Subverted in The Venture Brothers, where #24 takes off in a jetpack of the bottom-roasting sort (although it does have a plate that covers the length of the flames coming out), and off screen says 'My shoes are on fire! I just lit my shoes on fire!'
Averted in Roughnecks: Starship Troopers Chronicles, where the jets are mounted on heatproof Powered Armor, and used only for landing (slowing the fall rather than actually flying) after a drop.
Aversions in Batman Beyond, and Static Shock: Both Terry and Richie have jets, but they're mounted on their 'feet, rather than their backs.
- And by extension, any character that opts for Jet-Boots over a Jet-pack.
Also, the movie Batman: Mask of the Phantasm shows the Joker using a jetpack with exhausts on the shoulders.
Brought up in El Tigre, where Manny rejects BlackCuervo's We Can Rule Together offer with a jetpack for incentive. (Which Manny really, really wants) As Cuervo flies off, Manny tries to console himself by talking about this trope.

Cuervo: There's a cooling fan!
Manny: ...Dang.

Web Comics

Subverted in The Adventures of Dr. McNinja as Doc meets a man using a jetpack and immediately tries to treat his leg-burns. Apparently, the dinosaurs who sponsor the whole jetpack thing (it really does make sense in context) deliberately use this style, as they are hunting the humans and aren't particularly concerned about their well-being.
Averted in Homestuck, where John's Rocket Pack is so large that it extends to the floor, and the exhaust comes out below the feet.
- . . . but then played straight with Terezi's Wing Pack, which has the engine in the usual rump-roasting place.

Real Life

Real life jetpacks do exist. The exhausts are sensibly outboard of the shoulders, though, and not in position to set any assets on fire.