Why your teacher made a DMNPC as a boss is beyond me, but... being a knight is awesome in D&D 3.5, thank you.
I think the reason I don't have a lot of PK or TPK stories is because I've been in mostly level-headed groups that think tactically in tabletop games and don't try to murder each other. But now that you mention the knight/paladin shenanigans, I remember a story...
Once upon a time, I was playing Pathfinder. I was really new to Pathfinder and to the gun rules, and I've always loved playing paladins. Goody-two-shoes is my playstyle. So, I made a Holy Gun: a paladin with a pistol who was ready to shoot straight for justice! But I specifically chose to worship the deity of redemption because I didn't want to play your "EVIL MUST BE PUNISHED" paladin. I wanted to play someone who could get along with non-good party members and see past their faults. I wanted to play someone who tried to build others into good people.
My paladin's companions included a very zealous Lawful Good cavalier, an oracle whose details I forget, some other spellcaster, and then this roguish fighter type that was a little bit of a pragmatic edgemasterr. Important to note: the cavalier was being played by someone who normally played chaotic neutral doorknobs who kill for sport and the edgemaster was being played by his best friend. (I didn't play with these guys for very long.)
Well, long story short, our first adventure saw us fighting kobolds. We captured a few of them, and of course my paladin wanted to show them mercy. Now, the cavalier's player was kind'a new to playing good, so he latched onto my idea of "keep the bad guys alive" and was pretty fervent about this.
The roguish fighter was pragmatic, as I noted. He observed that we really couldn't go lugging these captured kobolds around. He actually had some good logic, too: first, dragging them around would slow us down, and we had a town to save; second, they'd try to escape; third, if they escaped they'd go get more kobolds; fourth, they would do their darnedest to make our lives miserable; and fifth, he was being in-character and his character didn't feel like kobolds were people. So, he wanted to kill 'em.
Remember how I said the cavalier was pretty zealous about this "don't kill the kobolds" thing? Well, as the fighter and cavalier were arguing about what to do, the fighter demonstrably just cut off the head of a kobold to stop the argument and get us moving. So, the cavalier charged him.
Now, cavaliers have this thing called a "horse." When you charge on a horse with a lance, you deal double damage. Because the fighter wasn't expecting this, the cavalier got a free round against him (according to the GM's ruling) and just rode the fighter down. BAM. Knocked him out in one hit. Then he was going to kill him...
The GM should never have let this scene get to this point, note.
So, me being the gentle paladin I was, I tried to shoot his hand so he'd drop his weapon and not kill the fighter. I didn't want to kill anyone - I just wanted to stop him from performing a coup de grace on the fighter. But, see, I'm a little famous for having really good rolls. I got a 20. I rolled damage with my pistol. I got max.
Did I mention we were level 1, our Oracle had used up all her spells, I didn't have Lay on Hands yet, and neither of us had ranks in Heal?
Needless to say, the cavalier and fighter both bled to death.
P.S.: Holy Gun is a trash archetype. Mysterious Stranger 1 / base paladin onwards is waaaaay better.
