Usually, borrowing without consent is called "stealing".
Some jurisdictions (like the question you link to) may not call it theft, but it is almost always illegal. Otherwise, among other problems, it would create a loophole rendering any theft de facto permissible.
At best you might convince the owner to retroactively exonerate you, by stating that he gave consent to the borrowing. But in theory the state could prove that at the time you borrowed the item, the owner could not yet have given consent, and therefore you did steal it - although I doubt that any prosecutor would bother with such nonsense, if the owner doesn't even wish to press charges. If they do press charges, you will have a very hard time with the "I was just borrowing" defense in court.
One might wonder, if you give it back before the owner knows, where's the harm? Well firstly you have no way of knowing the future, and the owner might end up suddenly needing it before you return it, so you are depriving them of the opportunity to use it: Imagine you "borrowed" a hospital's ambulance for a day. Second, you are putting wear and tear on the item, thus depriving the owner of some fraction of its useful life. You might even return it in a worse state that requires costly maintenance or repair.
I think one obvious exception to this is when there exists a mutual understanding of "communal goods". If everybody including the owner agrees that certain items are common use (like a pot in a shared kitchen), no indication was ever given that the item is not to be taken without permission (such as a sign) and the item is left unsecured in an unrestricted area, it would be very difficult to argue theft and prove it beyond reasonable doubt.