I found some more images of the flag of Diesel Island – Land of the stupid, Home of the Brave – that allow describing it slightly better.
(Nickname)

I found that it's really a more or less 2:3 flag, almost faded white over somewhat faded denim flag with a non-faded, shallow dexter edge triangle, with centred a greyish disk of cloth bearing the emblem of Diesel Island.
(Dream and dexter hoist side)

That emblem then is the Diesel head Elias mentions, with the top of the hair cut, the text DIESEL ISLAND, and two connection lines forming a circle around the head, with a second, continuous, circle surrounding that.

Their own description is:

Diesel Island's flag was created from three pairs of jeans put together, in order to represent different kinds of people coexisting in perfect harmony.
(A beautiful metaphor that we always have to explain because otherwise nobody gets it.)

Not mentioned is the fact that it's entirely in obverse on both sides.
(Description and sinister hoist side)

Those willing to view the Diesel Island videos may discover whether any further references are made to the flag, or whether it's mentioned in the Diesel Island anthem.
Peter Hans van den Muijzenberg, 3 January 2012