  We calculate the ratio eta/s, the shear viscosity (eta) to entropy density
(s), which characterizes how perfect a fluid is, in weakly coupled real scalar
field theories with different types of phase transitions. The mean-field
results of the eta/s behaviors agree with the empirical observations in atomic
and molecular systems such as water, He, N, and all the matters with data
available in the NIST database. These behaviors are expected to be the same in
N component scalar theories with an O(N) symmetry. We speculate these eta/s
behaviors are general properties of fluid shared by QCD and cold atoms.
Finally, we clarify some issues regarding counterexamples of the conjectured
universal eta/s bound found in Refs.[16,17].
