Let's see... I might be able to scare up a few stories...
I replaced the balancer on my '77 Corvette a few years ago. Got the trick puller tool from Summit Racing and pulled it off, no problems other than lots of grunting, getting a 20 year old part off the engine for the first (but not the last) time. Bought a new one from a Chevy dealer. Balancers come unpainted so you can paint them factory orange, factory blue, or whatever color your engine happens to be. Well, I had a can of blue spray paint that I had used to paint the valve covers. Apparently it had been sitting around for a while so the nozzle was clogged up. I thought, hmm, this is peculiar, and started messing around with it. PSSSSH! I nailed myself right in the face with blue paint. Fortunately I wear glasses so I didn't get any in my eyes... but I spent some time with mineral spirits cleaning off my face and my glasses (and I didn't even have a spare pair at the time).
Then there was the time that I finished installing $1100 worth of stereo equipment in the Corvette, and I had barely enough time to finish reassembling the interior before a friend and I were to leave for Hershey for the day. We were running very late, so as soon as I got everything together, I started the engine and off we went. Mind you, this was a car that had been sitting over the winter, and I did not bother to check the oil. Well, that turned out to be a really bad oversight. A week or so later, the engine developed a rod knock... apparently I had run it two quarts low and that sealed the fate of that engine. This incident kicked off a 3 year restification project on the Vette, because once I had the engine out, I found other things that needed to be done on a 25 year old car with 100,000 miles. There was an upside, though... I used the opportunity to replace the 180 hp base motor with a 390 hp small block.
Fast forward to the current day... so there I was, trying to track down an electrical short in my '70 911. I found that one of the red wires that attaches to the battery has a short to ground. I disconnected the wire and started using a multimeter to check continuity between the end of that wire and various locations under the dash. I unplugged the connector from the ignition switch, and I found that this wire apparently connects to multiple terminals in the connector. I then noticed that the connector has a cover on it, and I started wondering if there was a short inside the connector... so I unsnapped the cover, ever so carefully, to avoid breaking a 30 year old piece of plastic, and BAM! All the wires fell out of the connector. So there I was, with a 911 that still has a short, but now I also had munged up the wiring for the ignition switch. I'm still trying to put this back together, so if anyone has any ideas, I'd love to hear them.
http://forums.pelicanparts.com/showthread.php?threadid=131767
http://forums.pelicanparts.com/showthread.php?postid=995833#post995833