The only thing I can think to compare Pineapple Express to is Midnight Run, which similarly mixed action and comedy in an unconventional but symbiotic manner.
The dumb, bantering hitman and doublecrossing friends recall Midnight Run.
In a sense, this harkens back to the "buddy flicks" so rampant in the 1980s, odd-couple outings like 48 HRS. and Midnight Run (no wonder iconic '80s band Huey Lewis and the News was tapped to belt out the closing-credits title song).
In the end, the film is solid entertainment in the Midnight Run vein.
It seems appropriate subject matter for a comedy that is itself a unique blend of action and comedy, the kind of buddy movie that they made a lot more of in the '80s (Midnight Run, 48 Hours, etc.), but that has kind of fallen out of style now that the Farrelly brothers and Will Ferrell have replaced dark humor with the gross-out variety in the "adult comedy" genre.
Despite its rusty mechanics and hodgepodge of tones, Pineapple Express convincingly imitates the mode of Midnight Run: on-the-run odd-couple comedy with gunplay and car chases.