When did you realize you sent it a little too hard?

no it was fine

When I'm in a bad position for the next corner.

Many years, at a local autocross, I figured that if I took this one particular turn a bit wider than everyone else, I could maintain a lot more momentum.

When I heard all the gravel, marbles and debris bouncing off the bottom of my car as it started to spin off the course, I realized that it was no longer the hot setup.

Regarding what Pete said...

It was pretty quickly after I successfully passed that guy I-was-totally-convinced-I-could-pass going into the kink at CMP.  On one hand, I was correct in my assumption. I did pass him.  On the other, I was quickly reminded that not a place you want to be at pace and off the line. 

In reply to Matt B (fs) :

Oof. I made a pass going into the kink at CMP and as I settled into the line realized that a BMW had passed the same car on the right and we were headed for the same line out of the kink. He locked it up for a bit and I adjusted my line and we were fine but it was a brown shorts moment. I'm not sure how fast I was going then, but a prior GPS lap showed 110mph so it was not slow.

There was that autocross where I ended up pointing backwards in the stop garage and could still see people running away in the rear view mirror.  This was the result of a 90 degree turn at the end of the course and a "both feet in" situation.  Amazingly it was a clean run.

In this video, right about 17:45, and then again, not quite as badly at about 18:45.  

https://youtu.be/kPwoWxDf4y8?t=1064

Stayed in the throttle a bit too long in a slalom.  Glanced down as I lifted towards the end and saw something in the ballpark of 60.  I was sideways before I even touched the brakes with no hope of making the turnaround without something getting messy.  That was always my downfall of driving the Jeep in a rallycross.  Any tight, low speed course feature slow and often messy.  But the more open, faster sections of course were really fast, as it was one of the only cars in the field that had both enough power to get up and fly through those sections and enough tire to use that power (and would take a slalom well at speed). 

Started outside on the front row, left lane. Decided I had to stay even with the pole sitter all the way to turn 3 to have a chance to lead. At turn 2 ( right hander) the GTI lost the rear, spun 180*, and struck the inside curb with the left front wheel and began to go up on two wheels. At some point ( 2nd pic ) I looked out the side window at grass and realized it wasn't coming back down, at least not on its wheels. Two and a half rolls later it stopped on its roof.

v

I used to say that I had done every rookie mistake in autocross except hit timing.

Then we had a torrential rain at DeLand. I spun off coming through the finish and just caught  the box with the back of the car, but late enough to still get a clean run with a recorded time. 
 

One moment in particular when I suddenly realized I wasn't as good a driver as I thought at age 16 in my E30: ran out of opposite lock trying to save a slide on a highway off ramp and proceeded to beach the car in the pile of drainage stone at the bottom of the cloverleaf. That car taught me a lot about lift throttle oversteer, and about showing off...