I can think of two screw ups....
1. I bought Swift springs and decided not to listen to my buddies about paying a pro to do the install. I tried removing a 19mm nut from the front end of the car that holds the shock in place..... using a standard set of sockets. I ended up stripping it fairly bad so I mad a midnight run to Walmart and grabbed a set of 1/2" metric sockets. I was able to get the 19mm socket on the nut a tried to remove it. It just stripped it worse and so I take a quick look at it and realize I had purchased 12 point sockets...
. So at 1am to take another ride to Walmart and bought 6 point 1/2" metric sockets and I was able to pound it into place using a hammer and then attached the socket and it came off with ease.
Then while I was putting it back together(just about finished) I began screwing that nut back on with my fingers and got it finger tight and then used a breaker bar to tighten it since it was so difficult to get off I thought it should be rather tight, especially since it was part of my suspension. Needless to say, the nut never stopped spinning. I drove for 3 weeks with a stripped out nut without issues. I ordered both the nut and bolt that also goes to the sway bar because I wasn't sure which one I had stripped. The nut was like $2 and the bolt was $32 from Nissan. Well I removed the stripped nut easily just to find out that I ONLY stripped the $2 nut and the $32 bolt was not needed and Nissan won't take it back since it was special order.
2. I recently painted the inside of my headlights. Everything went nice and easy but then I used the larger of the tiny screws for inside of the headlights so by the time I got to the final steps of putting the bulbs back in I needed those larger screws because the extremely tiny ones that I had left would not catch at all. Luckily I'm a cable guy and I had a brand new splitter laying around and they come with the exact same size screws that I needed, so I was able to finish the job without any real issues.