When villains lose their cool (spoilers)

[Objectable]

Besides the every Actually GUilty person in Ace Attorney, I nominate Gul Dukat at the end of Sacrifice of Angels.

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And while its debateable that anyone except Kyubey is a villain, here is Sayaka going nuts.
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[RiseUp]

I'd bring up The Operative from Serenity. Though he never seems unhinged or psychotic at all, unlike the other villains mentioned in this thread, he's always so calm and collected, even taking time to espouse his philosophies to people before he (again, calmly) kills them. Near the end, though...

When the fleet of Reavers arrives, you actually see cracks in his armor. It really helps convey how much of a threat the Reavers were, that their appearance could make someone who seems to pride himself on being calm and thoughtful lose his shit.

 

[Johnny Novgorod]

I'm sure there's a sexual fetish in here somewhere....

A fetish about people losing their cool? Doesn't ring a bell at all.