  The [CII]158$\mu$m line is one of the strongest far-infrared (FIR) lines and
an important coolant in the interstellar medium of galaxies that is accessible
out to high redshifts. The excitation of [CII] is complex and can best be
studied in detail at low redshifts. Here we report the discovery of the highest
global [CII] excess with respect to the FIR luminosity in the nearby AGN host
galaxy HE1353-1917. This galaxy is exceptional among a sample of five targets
because the AGN ionization cone and radio jet directly intercept the cold
galactic disk. As a consequence, a massive multiphase gas outflow on kiloparsec
scales is embedded in an extended narrow-line region. Because HE1353-1917 is
distinguished by these special properties from our four bright AGN, we propose
that a global [CII] excess in AGN host galaxies could be a direct signature of
a multiphase AGN-driven outflow with a high mass-loading factor.
