Six feet under

You can check the definition of this idiom here.

a terrible show has the same name....

I don't want to be six feet under yet. I'm too young to be.8-)

to pop off or be a goner

another good american english idiom for that would be to buy a farm, or simply, to buy it. for example: he bought it during a skirmish with the jerries. also, when somebody dies, they croak. to give up the ghost, to kick the bucket, to fall off one's perch, to bite the dust, to pop one's clogs - all of these idioms mean to die in colloquial american & canadian english. i'm sure brits, aussies, and kiwies if not use, then are at least familiar with the expressions.

six feet under - is this idiom used formal or informal ( colloquial) speech?

Madox

Ok, in the meantime, I found the answer. It is used informal and in a humorous way.

e.g

These cigarettes will put Penelope six feet under.


Madox

I learn it from a name of a TV drama :-)

If someone is six feet under, they are dead as a doornail!

And certainly not just dead to the world. ;-)