WATCH OUT! WE GOT A BADASS OVER HERE!

[Dectomax]

Also, killing anyone in a helicopter in BF3, then watching it plummet .

Blowing a jet straight up with an RPG and have the burning wreckage land two feet behind you.

I nearly fell off my chair from the insane amounts of awesome.

I see your RPG Jet takedown and raise you a barrel-rolling tank and hitting some poor sniper in the process. It took me a few seconds to realise what I'd done and then I let out a roar of "YEEEEEEEEEEEEAH!"

That or taking out an enemy helicopter and getting a double kill and then getting a friendly fire. The wreckage landed on my team-mate. I laughed so hard. :')

 

[KiloFox]

boss fights in PSOBB... i modded the game to play Blue Dragon's "Eternity" as the boss music... every time i feel invincible...

any time my SATO MAG makes me invulnerable in PSOBB... i pull out my double saber and rush EVERYTHING unleashing just a Huney tidal wave of destruction...

whenever i have 1 bullet left in a weapon (usually a sniper, but sometimes an AR as well and i don't realize it) and i make a kill with that one bullet

and this one time in Halo Reach i made my Spartan 3 look like Sam Fisher in campaign... it was the Long Night of Solace mission (on heroic) in the bridge area (the control center) i was able to assassinate ALL the elites in the bridge then shotgun the face off the grunt... i felt like a god...

 

[ediblemitten]

Civil war questline, charging a stormcloak controlled fort.

Three stormcloaks suddenly run out to confront me at the top of the stairs. I charge up a power attack, and slice through all three with a single blow from my ebony greatsword, killing all of them.

 

[Erttheking]

Whenever I assassinate someone in Halo Reach, there is nothing quite like watching your guy jump onto the back of an alien that is a head taller than him and smiling in satisfaction as a neck is snapped.

 

[Patrick Corners]

In almost every Ace Combat where you have to fly through a tunnel. That can be pretty badass

 

[Beryl77]

All I've been playing recently is Saints Row the Third.

So, basically the entire game

This.
I've yet to play a part in that game where I don't feel like a total badass. For example, I just shot a bunch of helicopters down with two pistols.

 

[repeating integers]

It might not be that hard, but slaughtering an entire Firefight wave with nothing but a pistol on Reach makes me feel good. Real good.

 

[Fwee]

Grand Theft Auto IV Multiplayer:
I duck into an alley for the machine gun and turn to see an enemy car barreling down the street. He's coming straight at me, shooting out the window the entire way. My thumb twitches, hitting the jump button.
"I'm screwed," My neurons have time to fire through my brain. I see my character jump straight up in the air. The car smashes into the back wall and I land on top of it, stumbling slightly. His head is right between my feet! He realizes he hasn't finished me and starts to try shooting out the window as I unload the entire mag into the car.
Now I have a ride!

 

[Rensenhito]

Skyrim: dual wielding conjured swords against 3 bandits and a conjurer. Killing the conjurer with one of those slow-mo execution-style finishers, then killing both the bandits at THE EXACT SAME TIME with a critical-hit double swing. They were both bum-rushing me at the time, so it looked like I parted them with my swords, and they both fell to either side of me.
Bad. Ass.

 

[w1ndscar]

These three videos from back when I played Halo Reach made me feel warm and fuzzy inside.

I was in a 3v3 swat match, and my two team mates left me. So it was me vs 3 guys. I don't normally t-bag a lot, but these guys insisted on t-bagging me, so I got pretty aggressive. I also won, it was pretty great.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=11175316&player=xTechnoProx

In this one was a swat pistols match, and two guys were camping the elevator there the whole match, and I came in there and basically did this every time:

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=10653414&player=xTechnoProx

And lastly, this one was probably my favorite. My friend and I assassinated two enemy players at the same time right near each other.

http://www.bungie.net/Stats/Reach/FileDetails.aspx?fid=10516284&player=xTechnoProx

 

[Saltyk]

It's probably been mentioned, but clearing a room full of goons in Arkham Asylum or Arkham City without any of them ever seeing you just makes me feel like a badass.

That can be said in most any game that allows you to do that. Deus Ex: Human Revolution made me feel badass when I'd kill a room full of goons without any of them spotting me.

And in my beta time on TOR, I felt bad ass taking on groups of enemies and beating them all single handed. A friend of mine watched as I fought a group of about 5 enemies and after one Force Sweep, all but the boss was dead. All he said was "Did you just beat all those guys in one attack?" Yes, I did. Badass!

 

[Sozac]

Every time I play on Grand Bazaar in Battlefield on the attacking side I rush right with my shotgun with holographic and extended mags and one shot everything, plant the bomb, jump up on one of those crate things, go prone, and kill everything that comes in because either they don't see me or they come in the door I'm watching and get one-hit. then suicide after it blows up because they cant take me alive. >

 

[deleted126167]

DELETED

 

[ReinWeisserRitter]

This just made me think of elite grunts in Borderlands, which are actually called Badasses.

And depending on what he is, you probably do actually want to watch out for him.

 

[The Diabolical Biz]

Just because no-one else had posted it.

OT: My numerous badass stealth kills in Skyrim speak for themselves, but in particular I've begun stealth killing the Draugr at the end of dungeons before they get up. Oh, and I inadvertently Mehrunes' Razor'd Mercer Frey 3rd hit.

EDIT: Ooh, that's fun, I'm 1337!

 

[xanderkun]

Killing off one specimen for each round in the magazine of my pistol in a game of Killing Floor.

 

[MetaKnight19]

Defeating the Pokemon League and Champion with a Porygon2, Charge Beam was my best friend.

Playing BlazBlue online as a lowly Level 1 and beating a Level 12. To this day I still don't know how that happened...

 

[BlackEagle95]

Mount and Blade.
Bow and arrow.
Mounted.
One shot/head shot kill on the enemy lord.

Full Gallop.
Like a mother F***ing BOSS!

 

[Duck Sandwich]

A few days ago, I was playing Team Fortress 2 as a Medic, and I killed a Pyro with the Bonesaw.
Winning a 1v1 match in Starcraft 2 always feels awesome.
Finishing off your opponent with Akuma/Evil Ryu's Shungokusatsu is so very, very satisfying.

 

[Scabadus]

I forget the reasons and motivations behind it, but there's a section in Modern Warfare 2 (...I think, it might be 1) when you blow up a series of doors with C4 and burst through them as time slows down and you mow down everyone in the room. So fun.