V3's Bobby Jacks, who after scoring a headshot on another student while his back was turned, was named 'Bocelot' (a reference to Revolver Ocelot) by other handlers, who joked about him killing other students with triple ricochet shots, scoring headshots from halfway across the island, and firing his gun and killing a student in V4 a year later.
Furthermore: Nobody killed Bocelot. He just got bored.
John Rizzolo is just your average player, except a little more cunning and a lot more sadistic. THE RIZ!, however, is so entirely badass that he creates cliffs from nowhere and drop kicks anyone he wants off of them. His Rizzlefandom on the SotF Rizwebsite has gotten to the point where Rizzlehandlers, often discussing entirely unRizrelated things, will add 'Rizzle' or 'Riz' to their words.
Lance Vanguard and Zack Dynamite, two rejected names for Characters in v4.
A rejected Troll profile gave us THE GODDAMN BUBBA DOVER. It was a Scary Black Man, with Blaxploitation tropes. Rather than being annoyed, it backfired and the handlers of the board seized on this one instead, to the point where any mention of Badass characters is sure to mention him at some point or another.
Fans of Kilplix'sLeft 4 Dead vids will note that Con, despite usually just lighting his team (or mainly just Kilplix) on fire, has quite the fan base and is thought the be the definition of awesomeness. In fact, Con is so awesome, he could probably kill Chuck Norris with only one Molotov.
During the third Desert Bus for Hope charity drive Matt Wiggins turned down an offer for $500 if he wore eyeliner. Hundreds of ridiculous accusations were made about how evil Matt was, including that he invented Desert Bus, midichlorians, and canceled Firefly. Two public access Twitter accounts carried out the meme (Things Matt Did and Things Matt Did 2). He was eventually redeemed by a) promising to watch Battlefield Earth, and b) this.
The Pokemon-themed adoptable site GPXPlus has Cloysterman, a meme spawned from an entry in the site's Pokemon dress-up contest. If it punches you, you WILL die.
Felicia Day has a blog entry detailing the Tweets other people have made of these about her.
Ashly and Anthony's dad from Hey Ash, Whatcha Playin'? is the ultimate badass. Look at any of their videos on Youtube for confirmation, particularly Lips.
The eponymous Ninja of Ask a Ninja often makes astonishing claims about what he and other ninjas can do. Like how a ninja can go through a snowstorm without being hit by a single snowflake, or that they are faster than the speed of light. They are the speed of darkness. He also claims that he killed 4500 people in a day and that the Black Death was a ninja.
Agents of Cracked brings us The Chief, who, among other things, eats lead and craps bullets(so his toilet gets all...shot up, when he poops), rides a triceratops to work, drinks tiger blood milkshakes for breakfast(MILKSHAKES, FOR BREAKFAST!), and personally knows Die Hard(Not Bruce Willis, Die Hard). Turns out he belongs to a pantheon of other such Chiefs, all of whom are equally badass(Up to and including sexually assaulting a mountain).
In a meta way, SCP-682 from SCP Foundation is one. Stories about new ways of killing it always end up in describing how it made it stronger.
Alto Clef can't be seduced because his crotch is a hand, and that hand holds a gun.
The chef from Regular Ordinary Swedish Meal Time melts butter by screaming at it, peels potatoes with his teeth, chops food with an axe, and generally demolishes the entire kitchen (and the occasional assistant) in the course of making delicious food. It helps that he's very, very swedish.