The biggest game wrecker in golf is metal woods. J/K.

I've often heard it said that the thing that wrecked golf the most was the scorecard.

Now to answer the rest of the questions.

My round goes to pieces when I've been hitting the ball well all day, but then the dreaded slice appears with a vengence.

The worst thing I do is sway sometimes when I'm tired - and forget to sway back, taking 3" of dirt before the ball.