The action of swirling one's cape in dramatic fashion right before an announced exit, but doesn't necessarily require the actual presence of a cape to achieve the intended effect (see awkward arm swing but followed with an exit stage left and dramatic music). Usually preceded by a declaration of intent, ("Come dobby, we're leaving") and followed by an evil laugh.
Usually reserved for villains, but can also refer to would-be heroes who just want to look cool. The real utility of a cape, because let's face it, capes do nothing except make you look cool. Often results in the opposite effect.
Cartman from South Park: "Screw you guys, I'm going home..." (queue cape flourish)
"To the Bat Cave!"
"I am Count Dracula... *cape flourish* AH AH AH"