That (along with your previous quote, Mxy) is from the truly awesome Adventures of Buckaroo Banzai Across the 8th Dimension. (Currently streamable on Netflix; if you haven't seen it, you really owe it to yourself to give it a try. Note that it may take a couple of viewings to get your bearings, but it's totally worth it.)
I bought a copy of the out-of-print novelization on eBay a number of years ago, which includes an explanation (actually a couple of different explanations, both great) of why the watermelon was there in that earlier scene you quoted. And another really fun item: When New Jersey (Jeff Goldblum's character) is being introduced to Reno and Perfect Tommy, and he (New Jersey) is trying to act like he's a big fan of the comic books and knows them all, he mistakes each of them (in turn) for Pecos. And Reno, laughing, tells him, "Pecos is in Tibet." What he doesn't tell him is that Pecos is also female. :-)
New quote: (delivered deadpan) "Humor. It is a difficult concept."
Donut