An athlete in a race, an adventurer on top of a train, a Pirate boarding a ship, a cunning politician executing an amazing plan, a Loveable Rogue during a Sword Fight, a warrior during a Last Stand, two friends sparring--anyone facing an interesting and fun challenge with a reasonable chance of failure will sport one of these smiles. It's usually a bit forced, showing the strain and stress the user is under, and a there's certain edge of malice and aggressiveness to it, even insanity: a hint of Blood Lust, to be precise. It's very common against AntiHeroes type IV and V, especially if they are young and/or adrenaline junkies. It is usually coupled with a steady gaze, even a frown of sorts.