Oh, *these* moments, eh? I got plenty.
I remember killing off Sims in the Sims 1 and 2 by the buckets. Don't ask my why. I played a little more seriously for the third opus, but my "Ghost House"-themed lot required that I kill two full sets of Sims on the same lot. Fencing them off inside one-square rooms turned too sadistic for my tastes, so I turned to the testing cheats for help.
Then there's Oblivion, Fallout, Fallout New Vegas and other such games, where I'll invariably hit a sort of threshold where after a high immersion period, my desire to remain invested drops to zero. That translates to me robbing everyone blind in the Imperial City, turning God Mode on and going to work on the Imperial guardsmen. I'll go on a happy killing spree for a short while, then wonder what the Hell is wrong with me for not being able to play the game the way it was meant to be played.
I seriously wish you could do that in Demon's Souls. Just, y'know, turn unbeatable for a while and just enjoy the feeling of "progressing". Punishing difficulty's all well and good, but I still occasionally feel the need to be told I'm an unstoppable force of righteousness and shit.