The script I made for deployment, because existing solutions didn't "feel" right, required a lot of work and maintenance when we later had to add features and bug fixes.
Another script I made for building and deploying Java applications, because I didn't like Maven and Puppet.
The micro service I rewrote because I wanted to use my own favourite programming language. I introduced a lot of bugs that were already fixed, missing features and another language for my co-workers to learn when they inherited the application when I left.