The worst is when the rule they cite isn't a real rule at all, like Lennart Poettering's defense of systemd breaking on usernames starting with a digit, which i

The worst is when the rule they cite isn't a real rule at all, like Lennart Poettering's defense of systemd breaking on usernames starting with a digit, which is completely valid as far as the Linux kernel is concerned but he decided such names were ackshully against the rules and therefore systemd wasn't broken, bug report closed not-a-bug.