Feel free to chime in with yours. Mine (spoiler-free):

Facing a large spider-like not-quite-boss. Set up 3 conflagration traps, turn and run through them (can run through your own traps), laugh at the enemy, go to flick an Aard at him, and find out that Aard detonates traps. Self-immolation at it's finest. I think I minorly scorched the baddie though.

I was one shot (literally full vitality bar) by the Krayen on my first attempt. Not really sure what happened there as I certainly didn't take that type of damage on my second attempt.

Otherwise, less "best", and more "wanna tear my hair out", was when I was in the mine with the three dwarves, they somehow managed to block me into a corner with two mobs and no amount of pushing could get me out. :/ Suffice to say, after loosing all vigor to blocking, I sat there cursing companion NPCs, especially since they're all pretty uniformly worthless. :p