Pin-Pulling Teeth

The tough guy takes out a grenade and pulls the pin with his teeth, then tosses it to kill a bunch of mooks. It's a common trope in action flicks and war films.

In reality, grenade pins are designed to be hard to pull so they won't be pulled accidentally. Attempting to pull them with your teeth will likely result in some painful dental damage.

Straightening the pin in advance to make it easier to pull is certainly possible but it greatly increases the risk of mass casualty I Just Shot Marvin in the Face - style accidents.

Examples of Pin-Pulling Teeth include:

Anime & Manga

Italy from Axis Powers Hetalia attempts this method of detonation but throws the pin while still holding the grenade in his mouth.
- His brother does the exact same thing in a later episode, and Germany Lampshades this. Hilarity Ensues.
- Germany himself plays it straight to demonstrate for Italy.
Fullmetal Alchemist: Olivier Armstrong does this when she takes a grenade from a fallen soldier to attack Sloth. Lan Fan as well during the assault against Father near the end (more noticeable in Brotherhood episode 62).
Gunsmith Cats ups the ante by having the grenade held by the pin as well. It was only a Flash, however.
Combined with Did Not Do the Research in Laputa: Castle in the Sky when Dola pulls out a German "potato masher" style grenade and pulls the pin with her teeth. Potato masher grenades didn't have pins, they used a pull cord in the handle instead.
Ghost in the Shell: Stand Alone Complex. Batou does this a couple of times during the shootout in Kusanagi's mansion, though as a full-body cyborg his teeth might be a lot tougher than those of an ordinary person.
Also happens with the cyborgs of Gunslinger Girl during a Killing House training exercise.
Hanaukyo Maid Tai La Verite episode 7. While running away from a giant rolling ball, Ryuuka produces a grenade and pulls the pin with her teeth.
Ryouko in Spiral does this in the Carnival arc, although it's mostly to serve as a distraction than to do any real damage.
In Tokyo Crazy Paradise, Ryuji does this on his way to rescuing Asago and Tsukasa in volume three. While driving and (unintentionally) blasting strangely appropriate enka.
Neon Genesis Evangelion. Done beautifully for Misato's death scene in the manga. JSSDF soldiers approach her slumped and fatally-wounded body; she turns her head towards them, revealing a pin in the corner of her mouth. Misato then shows her executioners the hand grenade she's holding.
Misato Tachibana does this in an episode of Nichijou.
Spike does it while fighting Vicious's men in the Cowboy Bebop episode 5 "Ballad of Fallen Angels."
- He does it again in the finale, during his Storming the Castle moment.
Done habitually by Clair Leonelli in Heat Guy J
Puella Magi Madoka Magica - When Kyoko grabs Homura to keep her from Flash Stepping, Homura pulls a flashbang grenade out of her Bag of Holding and pulls out the pin with her teeth, forcing Kyoko back.
Fujiko does this in The Castleof Cagliostro during an escape. Her other hand is busy wielding an automatic pistol.

Comic Books

Jenkins does this while fighting cyborgs in Atomic Robo #5.
Mockingbird does this during a snowmobile chase in the first issue of the Widowmaker mini-series.
A standard in Commando and other books of that ilk.
Raphael does this a few times in the TMNT story arc "Body Count".
Elsa Bloodstone does in the second issue of Legion Of Monsters.
Nick Fury used to do this back in his Howling Commandos days. The page illo on the Howling Commandos page even shows a member of the squad doing it.
COBRA operative Gristle does this in a Taking You with Me moment in Infestation 2: G.I. Joe #2.

Fan Fic

Ash pulls the pins of some grenades he stole from Kaiza and then blows up a bridge to keep the Cloyster from attacking him and Dawn in Poke Wars: The Coalescence.

Film

In The Wrath Of God, one of the "heroes" is mortally wounded but grapples his killer -- then brings up one hand holding a grenade. Grinning into the other man's horrified face (at about four inches), he says, "Life is just full of surprises!" before pulling the pin with his teeth and holding the grenade alongside their heads. Boom.
Loki does this in Son of the Mask... with a little tongue too. Justified since he has cartoon-style powers and is a literal god.
Done by Leonard Smalls in Raising Arizona.
Clarence does this in RoboCop while playing Dick's recorded message for Bob, before leaving Bob in the room with the now-live grenade. He scores bonus creepy points by using his tongue to get the ring between his teeth.
A Better Tomorrow II: Happens all the damned time in the final mansion shootout.
Ahnold does this in True Lies, using a grenade as the opening shot of a huge firefight at the enemy's hideout after escaping from being captured. Guess he still had his Terminator teeth in place when he shot that film.
Saito in Inception, as part of a dream sequence that invokes a bunch of action movie tropes.
In the 2005 version of The War of the Worlds, Ray spits out the pins of a couple of M67 grenades he uses to destroy a tripod.
Starship Troopers. Dizzy Flores does this, then throws the grenade down a Tanker Bug's throat to destroy it.
Done during the half-track assault in the otherwise quite realistic 1945 film A Walk In The Sun.
GI Joe: The Rise of Cobra. Ripcord does this before stuffing the grenade into the face of an armored Cobra agent.
Major Payne did this to a live grenade when he threatens his cadets.
One of Deak's mooks does this in John Woo's Broken Arrow, due to one of his arms being all shot to hell.
Shows up in the controversial Errol Flynn WWII film Objective Burma, perhaps the only America Wins the War film made by an Australian. A number of WWII-era films compound this by showing both American and Japanese soldiers using this trope even though Japanese grenades did not use pins.

Literature

Richard Marcinko addresses pulling the grenade pin with your teeth in Rogue Warrior: Task Force Blue.

Yeah yeah, I know you always see the hero pull the pin out with his teeth. Well you try it sometime, if you want to send your dentist's kids to Yale. Because the only thing you're gonna get if you try and pull a fucking grenade pin out with your teeth is broken teeth.

Done during the climatic battle in the first Modesty Blaise novel.

Live Action TV

In an episode of Mash, Frank pulls a pin out of a grenade with his teeth and spits it away before panicking and desperately searching for the pin.
R. Lee Ermey addresses this in an episode of Mail Call, pointing out how doing this is a good way to lose teeth.
The Goodies references this trope when Graham bites the top off a pineapple which then explodes for no apparent reason.
Done in The Rat Patrol. See the episode "Truce at Aburah Raid" for one example.
Tested as a mini-myth on Myth Busters. Busted as it takes ten pounds-force to pull the pin from an M67 grenade, which is enough to break or uproot teeth. While people have pulled grenade pins with their teeth (see the Real Life section below), it is certainly not as easy as the movies make it appear.
Ace's nitro-nine grenades in Doctor Who are made from scavenged aerosol cans, so they have caps instead of pins. In a possible allusion to this trope, the Doctor pops the cap off one grenade with his teeth in Remembrance of the Daleks.
- One of Morgaine's knights does it in "Battlefield".
Michael Westen does this with a remote-detonator-on-a-deadman-switch (his words) in the season 1 finale of Burn Notice.

Music

"Detox" by Final Fight:

grenade over the shoulder
pulled pin in teeth
explosions forever

Newspaper Comics

In Beetle Bailey, General Halftrack once tried to do this as a "This is how we did it back in my day!" demonstration — but just ended up throwing the still-pinned grenade along with his dentures.

Tabletop RPG

Shadowrun. In the short story "Balance" in Shadowland magazine #6, a dwarf does this with a concussion grenade while fighting a gang of zombies.

Video Games

Persona 3: upon being defeated near the top of Tartarus, a wounded Jin stays behind and does this to blow up the Shadows climbing up from lower floors.
Fong Ling does this at the beginning of Resident Evil: Dead Aim.
Depicted on the cover of Ikari Warriors, a 1986 game for the Amstrad.

Webcomics

In a PVT Murphy's Law cartoon, Murphy takes a grenade pin in his teeth and thinks, "This is how John Wayne does it! Beat The Duke must have had a hell of a dental plan!"

Western Animation

When Wile E. Coyote tries it, the grenade naturally stays in his teeth.
In the Looney Tunes cartoon "Cool Cat", Egomaniac Hunter Colonel Rimfire tries to pull the pin out of a grenade with his teeth, but ends up pulling out his dentures and hurling the unarmed grenade at Cool Cat.
In the MGM Droopy cartoon "The Three Little Pups", the wolf did this, with comical results.
In the Looney Tunes short The Great Piggy Bank Robbery, Duck Twacy (Daffy Duck) does this before throwing a grenade at the villain Pumpkin Head.
Grampa Simpson is shown doing this in his flashback to World War Two in The Simpsons episode "Raging Abe Simpson and His Grumbling Grandson in "The Curse of the Flying Hellfish"".
In one episode of Avengers Earths Mightiest Heroes, Madame Viper pulls the pin out with her tongue, then the rest of her teeth. Because shut up.
- Justified because she's a Skrull.
Duke does this during the Russia infiltration mission in G.I. Joe: Resolute.
Batman the Brave And The Bold: Batman does with (with two grenades at once!) during the teaser to "The Eyes of Despero!".
Generator Rex: Hunter Kain does this when he drops a grenade to cover his escape in "Night Falls".
Batman the Animated Series: A SWAT cop does it in "On Leather Wings"; the very first episode.
Animaniacs: In "I Got Yer Can", an Escalating War with Slappy Squirrel causes Candie Chipmunk to do this; terrifying a pair of nuns before blowing herself up.

Real Life

The pin usually doesn't trigger a grenade. It is a safety device that prevents the grenade from being triggered accidentally. Not all grenades use pins and most modern grenades have three safety devices, usually the thumb clip, the pin, and the spoon.
From the Medal of Honor citation for Jonah Edward Kelley:

"Although twice wounded, once when struck in the back, the second time when a mortar shell fragment passed through his left hand and rendered it practically useless, he refused to withdraw and continued to lead his squad after hasty dressings had been applied. His serious wounds forced him to fire his rifle with 1 hand, resting it on rubble or over his left forearm. To blast his way forward with hand grenades, he set aside his rifle to pull the pins with his teeth while grasping the missiles with his good hand."

Done by Leila Khaled, one of the hijackers in the Dawson's Field hijackings in 1970, according to an interview she gave in 2000:

"So half an hour (after take off) we had to move. We stood up. I had my two hand grenades and I showed everybody I was taking the pins out with my teeth."

German "potato-masher" grenades are triggered with a pull string hanging from the base of the handle, and these could be pulled with your teeth.
Bill Mauldin mentions two variations in his World War Two memoir Up Front: The first was a soldier who straightened the pins to make them easy to pull, the second was a soldier who fastened grenades to his belt by their pins so he could just pluck them and throw them. Both are implied to be pathologically aggressive.