  The shear viscosity is an important characterization of how a many-body
system behaves like a fluid. We study the shear viscosity in a strongly
interacting solvable model, consisting of coupled Sachdev-Ye-Kitaev (SYK)
islands. As temperature is lowered, the model exhibits a crossover from an
incoherent metal with local criticality to a marginal fermi liquid. We find
that while the ratio of shear viscosity to entropy density in the marginal
Fermi liquid regime satisfies a Kovtun-Son-Starinets (KSS) like bound, it can
strongly violate the KSS bound in a robust temperature range of the incoherent
metal regime, implying a nearly perfect fluidity of the coupled local critical
SYK model. Furthermore, this model also provides the first translationally
invariant example violating the KSS bound with known gauge-gravity
correspondence.
