I wouldn't say procrastination "isn't irrational," but I think we can all agree that it's natural and troublesome.
Procrastination is generally an avoidance behavior -- it's a way to avoid some anxiety that we have attached to whatever it is we're supposed to be doing. We do something else to run away from the anxiety instead of working through the anxiety and coming out the other side.
Which is completely rational, because working through anxiety is painful, and it's rational to avoid pain. Right? Or am I missing something again?