A box that allows someone to write HTML and JS and have it appear verbatim on a web page.
A horrific idea, and one that’s surprisingly hard to implement, as any sane CMS will stop you executing random code onto a web page, and any sane framework would stop you building a form in a free text box to POST data.
Every time we tried to fight this he would say “but WordPress would let you do this”. He tried to petition his boss to rewrite an entire web site and application we’d just built and delivered to spec and on budget in WordPress because “it would be better”.