Wood chipper.
Chainsaws earn lots of respect from me but don't scare me so much as the things I'm cutting falling the wrong way do. Like onto my house or self.
I cut down a bunch of pines last year with my chainsaw and had a few moments of struggle trying to persuade stuff to take a different path falling down than it was wanting to.
My Dad taught me as a kid though to always be prepared for what your cutting to snap back or jump up on you. As a kid we had a few acres for our home and then a few more for some rental cabins on the other side of town and between snow storms and tornado's I spent a lot of time clearing out a lot of fallen pines in my youth.
Also table saws do freak me out in the sense that one dumb move and you can lose your fingers. Actually used to know a guy that had a few beers and made one dumb move while working on a table saw and lost the tips on 3 fingers. Freaked me out.
Working under heavy things that are jacked up also freaks me out a bit. I always use jack stands but still something deeply ingrained in me of fearing a car coming down on me and crushing me to death. Guess it's from seeing those damn "Faces of Death" videos as a kid and one of them being something to that extent.
But nothing really now days freaks me out more than being up high and feeling like I don't have safety.
I went up on my roof a few years back to clean off some pine needle build up around my chimney and it looked pretty safe from the ground/ladder but as soon as I got my feet on the roof I realized it was actually much steeper than I thought and the tar paper wasn't enough to keep me from sliding towards the edge. I truly felt like I was at any moment going to lose it completely and go flying off the edge and wind up with terrible injuries.
I yelled down to my wife to hold the ladder and it was so damn scary trying to get from that unstable situation to the ladder.
Really freaked me out more than anything in recent memory.
And to think, I used to laugh at my Dad when he'd be scared out of his mind of heights which I was a kid
I guess it's just a getting older thing that makes one really appreciate what falling from a height really means.