My manager suggested that we include a "stupid user mode" in our application.

Everyone seems to be happy with that :)

Lots of applications have that. All the good stuff gets hidden behind the "advanced" or "expert" mode setting.

Ours is called stupid idiot proofing mode when user is not following instructions. But pretty cool for bug reports. 😂😂

Every app should be in stupid user mode by default

I know nobody here is going to agree with me, but I believe that users are _not_ stupid. They just have much, much less context than you, and much less interest in paying attention than you assume. They also make simple mistakes.
But if thinking about users as stupid helps you make the app more user-friendly (e.g by hiding details in the "advanced" mode) then by all means do it.
(sorry)

@elazar Depends, some users are plain lazy and they just don't want to explore the software they are using.

@tahnik exactly. Just like a normal person.