Avenging Wallflower 

Primarily, a basic wallflower who displays a general persona of demure incapability, but is in fact, one of great physical and technical prowess. Generally possess' a vast amount of unheralded, unseen power and go out of their way to be meek and unassuming, at least until a dramatic confrontation of any kind occurs in their vicinity. Whenever any sort of oppressive or aggressive humans (Bullies, jerks, thugs, etc.) are near by and active, they will feel an unholy compulsion to leap into action, screaming and laying waste to all who oppose them with their incredible skills, simply to interfere in the situation and thereby feel that they've done something significant. After they have annihilated any and all participants, they will return to their previous passive state.

Don't beat on Mike; He looks like a nerd, but I hear he's, like, an avenging wallflower.

Avenging Wallflower by Raphe and Erik Wojik November 10, 2008