Ever drive a car that was so fast that it scared you?

I'll start with one that maybe didn't scare me but took my breath away as it was just so quick for its time: Supra Turbo. 

I drove a 1,000 + HP Z06 Corvette that scared me.  It wasn't the horsepower so much as the poor calibration that didn't always close the throttle then you released the pedal.

The first time I drove a Northeast Dirt Modified it got my attention as well.

Modified 911 turbo with a manual transmission, allegedly a bit over 600 wheel horsepower. An older one that didn't have traction control, or if it did, it didn't work. At least on the street, it was just too much. Hit the throttle in lower gears and it was on the limiter instantly, and pulls in higher gears where it would actually hook up were beyond extra-legal. The turbo lag really kept you on your toes if you were trying to drive in the midrange rather than just cruising or really pushing hard where the turbo would spool quickly. I'm sure it would be fun on the track or a drag strip but it was just too much to be usable on the street.

This is an odd one, but:  A Nissan Maxima.

I had one as a rental.  It wasn't that the acceleration scared me, it was when I got to speed I became immediately aware of how terrible the tires/suspension/brakes were by comparison.

289 Cobra. The real thing.

Only in America would some idiot think that thing needs a 427.

Got through exactly one track event with ~400hp and decided that was a good way to get going way too fast way too quickly with relatively limited safety gear.  Went back down to 200whp track cars and am much happier.

Car, not really. 

Bike? Yes, a 2006 Honda CBR1000RR with no traction control and no ABS was ferociously scary on a cold wet day at Grattan with riders crashing and dropping antifreeze all over the place. It's the only time I've had one wheel locked and one wheel spinning simultaneously. 

A very modified FD. Huge turbocharger. 740hp on the dyno. When the boost kicked in at 4500 RPMs it was almost impossible to keep the rear tires in contact with the road. It was pure misery to drive on the street but that 4500 to 8000 pull was guaranteed to get your heart rate up. You knew it was trying to kill you, but you had to do it anyway. 

900ish HP 2013 GT500, every time I drive it I both love it and can't wait to give it back.  Laying stripes at 90-100 MPH accidentally is not always fun.

Every big bump up is a little unsettling at first. After a history of small, light cars hovering around 100hp, the 220-hp-according-to-internet-recipe swapped E30 was a little alarming at first. Similarly for the 265hp WRX though obviously that's a very composed package.

I got used to both of them pretty quickly, though I would say that on the street you only ever get to use that for a few seconds here and there. I mean, at some point I'd love to drive something with 1000hp and AWD just to giggle after tiny pulls into hyperspace, but I don't think that's where the fun necessarily is. In real-world driving around mode, the E30 was more than capable of overwhelming the stock size tires, and if it was, say, raining in Portland, and I was on the half of the roads paved in old concrete with all the aggregate polished, it took some attention to make more progress than wheelspin when merging from a stop.

Oh, and the Aprilia RSVR, though that's not a car. That took longer to get used to. It felt like the engine didn't notice there was a bike and a person attached. I was also, again after cars no faster than the E30, not calibrated to see turn one at PIR approaching that quickly. I just had zero experience with the phase of deceleration from 135 to corner entry... (Yeah, someone making a better exit off of turn 9 would have been arriving a lot faster than that, too...) Slow cars also don't prepare you for the sensory experience of sticking your head into a 135mph wind blast just when you're trying to concentrate on smooth inputs.