Give them an ability that works like Fax's Paladin Mantles.

The Badass is an exemplar of kicking ass and taking names. A Badass must choose at least one (and no more than his amount of Badass levels) spell slot of his highest level, one us of an X/day ability, a "special" charge in a wand or similar limited resource. After using such that ability, the Badass is fatigued after 1 round. If the Badass wastes the designated ability on stupid crap, he loses the benefits of this Mantle and cannot use that ability until he atones.

At 1 level of Badass, the chosen ability can be activated even when the Badass would normally be prevented from using it (in an Anti-Magic field, dazed, etc). This may not bypass being unconscious or dead.
At 2 levels of Badass, all foes witnessing the use of the ability (whether by mundane or magical senses) become dazed, even if they are normally immune.
At 3 levels of Badass, the chosen ability takes one shorter magnitude of action to perform (Immediate<-Swift<-Standard<-Full Round<-1 round<-1 minute) to a minimum of Immediate.
At 4 levels of Badass, the chosen ability can be used twice for the price of the one charge, but the Badass is unconscious after using it.
At 5 levels of Badass, the chosen ability may be used even if the Badass is unconscious or dead. The Badass receives one turn in which to act, and then dies. Only a True Resurrection, Miracle or Wish can bring back a Badass that uses this ability.

A Badass may atone by single-handedly slaying a foe of equal CR while heavily disadvantaged, such as in an AMF.