(since this thread is about English- I'll write in English )

the idiom "Elephant in the room"... is likely to have been invented in America and is used there far more than any other country...

The Oxford English Dictionary recently added an entry for this idiom- but they do not give its etymology....

the earliest 'official' source seems to be from 1984- a book entitled "An Elephant in the Living Room: a leader’s guide for helping children of alcoholics"

but I'm sure the phrase is older than that....

the 800 pound gorilla phrase is an old joke... I remember telling it as a kid back in the 70's... which probably means stand-ups were telling it in the 60's...

I have no idea how or why these two phrases could have been inter-twined....

I suppose (as others have) that it is a blend of those two powerful modern movements- ignorance and illiteracy....

and now....

it is back tae Scots fur me!

cheers