The phrase "entirely stupid" is correct and usable in written English.
It is typically used to describe something or someone that is completely foolish or lacking intelligence. Example: "I couldn't believe the entirely stupid decision the company made to raise prices during a recession."
They're not entirely stupid.
They can't be entirely stupid about politics because you don't get to be prime minister by knowing nothing about it.
It wasn't entirely stupid — profits and revenue are flawed, limited measures, and market value does tell you something useful about a company.
On the other, he is far from an entirely stupid man, certainly not by the standards of most Big Brother contestants, compared with whom many amoeba take on the intellectual sheen of Mary Warnock.
In John Ford's 1957 movie The Rising of the Moon, an English tourist, seeing injured players carried by on stretchers, asks nervously: "Charles, is it another of their rebellions?" The question was not entirely stupid, for the GAA undoubtedly was part of a cultural rebellion that could not be cleanly separated from a military one.
When discussing Billy Elliot: The Musical, their first venture into theatre production, now previewing in the West End, they jokingly catalogue other films that could be turned into musicals, from Fargo (definitely a joke) to Hudsucker ("not an entirely stupid idea", according to Fellner), to Bridget Jones, which gives Bevan a momentary glint in the eye.
Sanity seems not to be an entirely random or stupid social obligation, but never mind.
Often used sarcastically when one does something entirely mundane or stupid YouTube – the website responsible for Justin Bieber Zynga develops social games that are playable via app or on social networking sites, rather than traditional games consoles.
Channel TV admitted the breaches were "entirely unintentional but nonetheless stupid".
Channel TV apologised for the "entirely unintentional but nonetheless stupid" voting breaches, but called for Ofcom to bring in the police to investigate the switching of the people's choice award winner.
No one was seriously injured or killed when Sophia Anderson did something incredibly stupid and entirely preventable.
