Special:Preferences contains a big fat red link, "Restore all default settings (in all sections)" right next to the "Save" button. Thankfully, clicking that link brings you to a confirmation step instead of actually executing. However, this is //extraordinarily bad// user experience design.
I actually know what I'm doing and I spent a full 60 seconds deciding whether or not I should click that button before doing so. I was //pretty// sure that no one would be dumb enough to develop a feature like that without requiring a confirmation step, but I //couldn't// be sure.
1) This feature should be inside of its own tab, "Restore Default", which consists of a single block of text and a **large** warning icon. The button itself should be bright red, and there should be a "No thanks, take me out of here" link.
2) Clicking the big red button still shouldn't flatten the user's preferences; it should go to an additional confirmation step before that happens.
Some thoughts:
* There's a reason you haven't seen <input type="reset" /> used anywhere since 1998
* There's a reason "Restore to factory default settings" is buried deeply on mobile devices
* This should be a rare action, so making it front and center (bright red on every page) doesn't make any sense
* A destructive action of this type should never be placed in such close proximity to a constructive action ("Save" [save _what_, I might add])
* A destructive action of this type should always be quarantined and isolated.