[zahlman]

"It is dangerous to operate recursively on '/'" is such a stereotypically traditional Linux way to explain the situation.

(I would write something like "Refusing to delete the entire filesystem (did a shell variable expansion go wrong?)".)

[rpigab]

There's worse:

"Out of memory: Kill process or sacrifice child"

[Linux-Fan]

Reminds me of https://xkcd.com/293/