Walter against the nihlists in The Big Lebowski
Norma Rae holding up the “UNION” sign.
The Littlest Killer Klown from Outer Space taking on the bikers who trashed his scooter. 
From the other side:
Darth Maul, a Sith apprentice, taking on a Jedi Master and apprentice simultaneously. Of course, he later demonstrated he had mad skillz, but it still wasn’t a fair fight.
“You fool. What you fail to realize is that without your armor my ship will tear through yours like tissue paper.”
“Yeah. Well, what you fail to realize is… I’m dragging mines.”
Gabriel Byrne in Miller’s Crossing, during basically the entire movie.
In DS9, Kira is in command of the station, and she only has 4 photon torpedos. A Klingon (?) fleet is approaching and she orders that all 4 photon torpedos be shot across their bow as a warning shot.
J.
Snopes says this is undetermined, but I think this counts as pretty nervy of the British. 
I must second this. This is the coolest game of chicken I’ve ever seen. The pure confidence in Tim Allen’s voice and expression, the sudden panic when Sarris realizes what’s happening…considering Galaxy Quest is supposed to be a lighthearted jab at Star Trek and its fanbase, this wound up being a really badass scene.
Quick Change, when Grimm, Loomis, and Phyllis accidentally walk into a mobster hideout, and they need to not get themselves killed for it.
“We’re here… for the money.”
One of my all-time favorites: Clint Eastwood as Will Munny returning to Skinny’s place in Unforgiven. He walks alone into a saloon filled with armed sheriff’s deputies, carrying a double-barrel shotgun and a holstered six shooter. He makes his presence known with, “Who’s the fella owns this shithole?” And when his second shotgun shell misfires, he drops to one knee and levels the lot of them.
Little Bill: I don’t deserve this…
Will Munny: Deserve’s got nothing to do with it.
Little Bill: I’ll see you in hell.
Will Munny: Yeah. <BLAM>
Geena Davis in many scenes in The Long Kiss Goodnight. I especially liked the one where she’s tied to a water wheel and being drowned, and before she goes under she tells the bad guy that she’s going to kill him slowly (or something like that). Then underwater she gets free, finds the body of her friend who still has his gun in an ankle holster, takes the gun, comes up and kneecaps the bad guy.
Sanjuro in Yojimbo, chewing on a toothpick and calmly facing down three thugs with forty or so more behind them:
Sanjuro: You’re all tough, then?
Gambler: What? Kill me if you can!
Sanjuro: It’ll hurt.
It did, too.
Oh, I forgot Mel Gibson in Lethal Weapon, where he’s all tied up and being electrocuted. He shouts at Gary Busey that he’s going to kill him, and then when he has the opportunity he breaks the neck of his torturer with his feet, escapes, kills a bunch more people, then hunts down Busey. When he finds him, there are cops surrounding him but Gibson waves them off so he can take down Busey man-to-man with no weapons. Good stuff.
Philip Seymour Hoffman in M:I:III. Cruise has him captured and is doing all these high strung interrogation techniques (including dangling PSH outside the plane), all the while, Hoffman calmly sits there, saying, “You have a wife? Girlfriend? Somebody? Because I’m going to find them and kill them in front of you.” Hoffman then proceeds to do exactly that, then he hooks up with Travolta’s character from Swordfish, and they promptly go out, hunt down Bin Laden, blow him to bits, before moving on to their next target.
Well, that’s the way the film should have ended.
Stephen Maturin performing an operation on himself to remove a bullet from his abdomen in Master and Commander: Far Side of the World was pretty damned nervy. I always skip over that scene because it gives me the willies.
Ah, but it wasn’t even an ankle holster. The guy had told her earlier that he always kept two guns on his person. One in an ankle or shoulder holster, where it would easily be found, and the other, um, someplace where a guy wouldn’t get frisked by another guy. And I, too, was impressed by her ability to remember that and retrieve it in the alotted time.
My nomination: Reggie Hammond in the redneck bar in 48 Hours.
Just after the prisoners enter a concentration camp in Life is Beautiful, a burly Nazi guard comes into the barrack and calls for a prisoner to translate for him.
When Roberto Bernini raises his hand a worried onlooker quietly asks if he speaks German. He shakes his head no, stands next to the guard, and “translates” his speech of warning into game rules for the benefit of his son.
The first time I saw this scene I was at once laughing and astonished at the brass of this character. Fictional, I know. But it worked for me.
=Final scene of Butch Cassidy and the Sundance Kid
=Cedric the Entertainer as Eddie in the riots flashback of Barbershop 2
=Grandpa (Old Lodge Skins/Chief Dan George) walking “invisible” through Custer’s troops in Little Big Man
=Depp’s “Hello Beasty!” at the end of PotC2
Even though I didn’t like the movie, Harrison Ford’s jump to freedom off of that drainage pipe in The Fugitive was pretty ballsy.
The crew of the airplane in Operation Thunderbolt should get special mention since it was a true story. The hijackers are releasing all non-Jewish hostages and sending them home. They will start killing the remaining hostages once the deadline for their demands pass. As Israel has a well-known and strict policy of not negotiating with terrorists, the situation is dire. Yet the pilot of the airplane convinces his entire crew that they will remain with the Jewish hostages because they were entrusted with the safety of ALL of the passengers on his plane. Therefore, their job is unfinished and the pilot matter-of-factly tells the lead hijacker that they will stay put. Hijacker says, “Have it your way.” Balls. Of. Steel. Naturally, the crew was punished by their airline when they got back for unnecessarily placing themselves in greater danger. :rolleyes:
De Niro’s scene wgere he does the same thing in Ronin, and does it better, IMHO.