The most well-developed NPC the GM has, with an extensive back-story, detailed motivations, a deep and flavourful character portrayal, and also just inherently cool, and the PCs go and do this to him in their first real encounter.

Typical.

The GM's lot is a hard one.

Transcript

Darth Maul: So what's it gonna be, kid?
Obi-Wan: Helping Palpatine bring peace to the Galaxy would be good...
Obi-Wan: But a Jedi knight is bound by honour. I promised to return the Lost Orb to the Gungans.
Darth Maul: Ah well. In that case, seeya round. I got an Orb to get.
Obi-Wan: I'll report this to the Senate! The Gungans are the legitimate owners!
Darth Maul: Well now, that's a shame. If you're gonna squeal, that changes things. I'll have to bump you off first.
Obi-Wan: So it's you or me, is it?
Darth Maul: It's over, kid. I have the high ground.
Obi-Wan: You underestimate my power.
Darth Maul: You got some real chutzpah there—
{Obi-Wan suddenly leaps out of the pit, over Maul, and kills Maul with Qui-Gon's laser sword}
[SFX]: Sliiice!
Darth Maul: {dying words as he falls into the bottomless pit, bisected} And to think... I was gonna retire after this case...