  Graphene moir\'e superlattices display electronic flat bands. At integer
fillings of these flat bands, energy gaps due to strong electron-electron
interactions are generally observed. However, the presence of other
correlation-driven phases in twisted graphitic systems at non-integer fillings
is unclear. Here, we report scanning tunneling microscopy (STM) measurements
that reveal the existence of threefold rotational (C3) symmetry breaking in
twisted double bilayer graphene (tDBG). Using spectroscopic imaging over large
and uniform areas to characterize the direction and degree of C3 symmetry
breaking, we find it to be prominent only at energies corresponding to the flat
bands and nearly absent in the remote bands. We demonstrate that the C3
symmetry breaking cannot be explained by heterostrain or the displacement
field, and is instead a manifestation of an interaction-driven electronic
nematic phase, which emerges even away from integer fillings. Comparing our
experimental data with a combination of microscopic and phenomenological
modeling, we show that the nematic instability is not associated with the local
scale of the graphene lattice, but is an emergent phenomenon at the scale of
the moir\'e lattice, pointing to the universal character of this ordered state
in flat band moir\'e materials.
