As above really. What is the shortest amount of time it has taken anyone to wear out a drivetrain? I don't mean break a chain, I just mean wear out to the point of slipping and general uselessness…

So wearing the cogs down or breaking part of the machinery?

I've broken brand new BB's in the car park. Lots of people have. It's called 'ISIS'.

I guess under normal circumstances, I've worn out a chainring in about 6 months on a mountain bike.

This took me about a year though.

6 months, full LX drivetrain (chain, cassette, two chainrinhs, middle & inner) on my first real mountain bike back in 1996. Kept on applying lube without ever really cleaning any off. Was also using a wet lube year round, and "didn't" know that chains needed replacing!

Since used a Rohloff chain checker regularly and change chains as needed.