Once rebuilt a b18 and started it up. No amount of adjustment on the SU's would get rid of a weird pop and it was slow as shite. Tried to figure it out for a week, drove the car 80mph on the highway. Turned out I had switched 2&3 plug wires through a series of compounding mistakes. The amazing thing was that the motor ran so smootly on 2 cylinders that I did not even suspect the firing order.

I also installed a flywheel backwards on a 327 once. After a month of driving it started to make nasty noises. When I finally pulled it apart the flywheel had fractured in a circle along the bolt pattern. I was revving this motor out to 6500 rpm, a hair's breadth from sending my flywheel on a deadly buzzsaw rampage.

A friend had a chevy with a press fit harmonic balancer. He did a lousy job pressing it on and revved up at a stoplight (manual transmission). The balancer let go, shot through the hood and landed in the opposite lane in front of a state trooper. Jailarity ensued.

Once Left a dirty rag on the header after an oil change resulting in a fire in a department store parking lot around xmas. The fireman jokingly said 'some guy at the jiffy lube left it, right'. I nodded in shame. Was able to drive the car home, but the melted ignition wire insulation made it interesting.

Forgot a castle pin in a balljoint nut - popped and lost control of a front wheel going 35.

Dash fires, busted oil pressure line spraying in the passenger compartment on a first date,once hit a curb too hard and turned my steering linkage inside out (I still don't understand how this happened, either).

Those are the ones I will confess too...