It was a production prank. That's it.note Word of God states they literally put it there to get up the nose of a particularly pushy film executive who seemed to hate everything about the film, so they put a watermelon in to see if they could get a rise out of him, and figured out of it that he'd stopped watching the production work.
Cult Classic: The film has a devoted following among those who found it on broadcast, cable, and VHS tapes.
Genius Bonus: When he first meets Reno and Perfect Tommy, Jersey mistakes each of them for Pecos. Later comics reveal that Pecos is a woman.
Ham and Cheese: Everyone in this film seems to be having the time of their lives, but especially John Lithgow. The fact that everyone went so far over the top is probably why it has retained the cult status it has instead of being entirely forgettable. In fact, in an attempt to actually produce the announced sequel, Buckaroo Banzai vs. the World Crime League; all of the former cast were reported as being enthusiastic about returning to their roles. Unfortunately, the film remained stuck in Development Hell.
During the opening credits (When William Traylor and Carl Lumby's credits are on the screen), there is a square yellow box equipment-thing in the background, with what look like two white eyes and brown for the lower third. It really looks like Spongebob Squarepants, though could never have been intended to. This wouldn't even be worth mentioning save for the fact that Clancy Brown (Mr. Krabs) plays Rawhide. Funnily enough, Buckaroo Banzai actually got a Parental BonusShout-Out in one 2000 episode of SpongeBob SquarePants ("Big Pink Loser"), where Patrick claims that his life's dream is to "defeat the giant Monkey-Man and save the 9th dimension". ("Monkey Man" was John Bigbooté's disparaging term for humans)
Buckaroo's suit during the end credits looks a lot like Peewee Herman's outfit. Although Paul Reubens was already something of a cult figure as Peewee Herman, it wouldn't be till the next year with Pee-wee's Big Adventure that the character would catapult to national consciousness.