  One of the hallmark properties of fluids is their shear viscosity which is,
among other things, responsible for parabolic flow profiles through narrow
channels. In recent years, there has been a growing number of observations of
said flow profiles in electronic transport measurements in a variety of
material systems, most notably in graphene. In this paper, we investigate the
shear viscosity of interacting graphene from a theoretical point of view. We
study both a phenomenological as well as a microscopic model and find excellent
agreement between the two. Our main finding is collective modes make a sizeable
contribution to the viscosity that can equal or even outweigh the electronic
contribution that is usually assumed dominant. We comment on how this finding
carries over to systems beyond graphene and related Dirac materials.
