Here’s a paladin being killed by a clothie and saved by a DK.
(1) Darth Vader Kills Emperor Palpatine Scene [4k UltraHD] - Star Wars: Return of The Jedi - YouTube
Probably a Darth Vader xmog out there that only a DK could pull off…
Darth Vader - Outfit - World of Warcraft (wowhead.com)
He’s probably Anduin’s father.
Some of my favorite player gameplay stories center around Death Knights.
-The thread with the raid leader complaining how the Blood DK spent an hour finishing the last raid boss himself after the party wiped the 3rd time…
-The PVP story the worgen DK told about the opposing team taunting them from the roof of a building they couldn’t get to. ‘Their leader stepped up to the ledge to laugh at us. I deathgripped him. We tore him apart.’
That said, my I’ve had some legendary experiences with Paladins.
-I was a Veng DH fighting a Paladin up on Highmountain and he was clobbering me, so I jumped off and glided to safety on the other side of the river. Paladin fell out of the sky and killed me. It was very much the sound and feel of an anvil falling on my head. 
-Playing a prot pally myself and suriviving murlocs indefinitely or killing rares and elites I bungle into unprepared.
I have some good bm hunter and demon hunter stories too.
I think the Blood DK solo’ing the last boss of a raid after his party wiped takes the cake though.