"based on or in accordance with reason or logic" / "able to think sensibly or logically" / "endowed with the capacity to reason".
You made the claim that you do not believe people are rational. Following from this you would also have to believe that individual's actions are without reason. Consequently, any perceived reason or logic, either by the actor or an observer, would actually be a post-hoc explanation for action. From a behavioural persective cause and effect would no longer exist, nothing could be predicted and nothing could be planned.
This is entirely at odds with what we know about post-truth. Individual behaviour can be modelled and population behaviour can be predicted to a degree.
Irrational actions do not imply irrationality. An irrational action is usually a consequence of rational thinking based on incorrect information.