In the early kernel (think pre 1.0), I “fixed” the CPU scheduler for performance. I gave too much privilege to user processes, who refused to relinquish control back to the OS.
Another time I was working on a multiprocess bootup configuration (before systemd) in a configuration where the main process would orchestrate the workers. Well, the main process would fork a child to do the work, then the child process would fork a child process to do it’s work. It was infinite delegation and I ran out of pids.