As someone who thinks Planes, Trains and Automobiles represents a peak of buddy comedy (if not Everest, at least a Kilimanjaro), Due Date was a knockoff. A pretty good one, but a knockoff just the same.
But what should really flip our noodle is this: If I saw Due Date before I saw Planes, Trains and Automobiles, would I think the opposite? Would I wonder why Steve Martin is trying so hard to be Robert Downey Jr.? Hmmm ….
What we experience first often becomes the template through which we view everything that follows.
The coffee can Donny, for example, will forever be his own template.