Rarely a primary antagonist, Unhinged Villain (example here -- there's a lot going on but watch the guy with they funny eye) usually takes the form of a Villain Of The Week or a sidekick, with his role often overlapping with that of Snivelling Henchman.
His demented, sociopathic behaviour, hammy overacting and tendency to lash out, often with fatal consequences, at innocent bystanders and expendable underlings alike may occasionally make the casual observer wonder how he ever rose to a position of power and influence in his evil organisation in the first place without getting done in, Joe Pesci-in-Goodfellas-style, by his colleagues.
While he will sometimes behave in a deceptively calm and composed manner, he is generally easy to distinguish from colleagues such as Misanthropic Villain and Philosophical Villain by his deployment of the Crazy Voice. This, coupled with his advanced case of Battle Loquacity, makes him one of the more annoying antagonists. If you ever come across a fight between Unhinged Villain and Pure-Hearted Hero, the volume control is an invaluable tool for the dedicated sailor of this most infuriating of anime seas. Failing that, a heavy boot to the TV screen usually suffices.