Parry is hard capped at 120.0. If it could go over that, it would get insanely difficult to land hits on that creature. A creature with 120 Parry has a 20% Parry chance. A creature with both 120 Parry and 120 Bushido has 35% Parry chance (creatures parry with the equivalent of a 1H Wep).
This is why pets that have Bushido (Magical), or Feint/Nerve Strike/Bladeweave (which give passive Bushido skill) can be especially tanky. I tank Exodus with a Feint Triton, one of the few pets that can tank Exodus for a long time and survive.