Ok, I've done this here before, but I'll do it again. I've done a lot of study on it, from the mid '90s on, primarily as part of the first website to document it, that set the stage for all of the popularity of the term since then.
First, we've had customs as long as there have been cars. Cosmetic changes to make your car more personal have been a staple of the car industry from the beginning, whether it was coachbuiilders building complete new bodies on factory chassis, to local garages giving a car a non stock color. As with a lot of things in the automotive industry, it really took off after WWII. You would see after that point a lot more "popular" custom tricks on street cars, from chopped tops to shaved handles and emblems, extended rear fenders, integrated skirts, extreme lowering, rounded hood and door corners, frenched headlights, trim removal or swapping, grille swapping, taillight swaps (which is why Altezzas are NOT rice, but merely the continuation of a decades long trend of making your personal car a custom). A '50 merc, lowered 4", with '53 Buick sidetrim, '55 Desoto grille, '53 kaiser taillights, extended fenders, Olds Fiesta huibcaps, etc, was not trying to be any of those cars. It was trying to be a custom.
Ok, that out of the way...
in the '70s, Japanese cars, which had been a small part of the American market for a decade already, started to become VERY popul,ar. With the gas and insurance crisis of teh early '70s and peole turbning to smaller cars, the well built japanese cars were a primary choice. The sports car crowd tat had been heavily into cars like the Alfa sedans, Mini Coopers, and the like started buying 240Zs, Datsun 510s, Mazda RX2s and RX3s, Toyota Corollas, and Honda Civic 1200s. These were not only well built street cars, but capable race cars for roads racing and autocross. At the time, American musclecars were either stock, or just used up old cars, or jacked up drag race looking things that weren't really all that fast OR well built. A lot of peole were finding that these small engine japanese cars were easily as quick in a straight line as well as capable around corners.
At the same time, another little import was gaining in racing popularity. the VW Bug owners had formed theri own racing organization and were holding HUGE custom shows. the bugs lended themselves to the same mods as street rods and customs, as well as drag racing. people were turning to imports like crazy.
Japanese bikes had made inroads into the american market as well. Harley and Trimph riders called them Rice Rockets, and had since the '60s when Honda and Yamaha had started winning a lot of races. That appelation was given to the fast japanese cars of the '70s by drag racers and rodders, as well. But contrary to someone's recollection, no one at the time called them ricers or riceboys.
Those of us driving and racing those cars (like my RX3) wished they were more popular and that people would see there was more ways of going fast than buying expensive Euro cars or American drag racers. Little did we know what would happen if our wish came true...
A couple things happened at that point, the convergence of a number of separate threads. One, the lowrider movement spawned a group built around minitrucks, and large truck clubs grew up in the '80s with huge shows. There was a lot of similarities to teh bigger VW shows (many were organized by teh same people). Cars weren't allowed in most of the truck shows, but the truck clubs often had cars built the same way (they were called Mascot Cars in the publications). Lowrider japanese and American compacts primarily, but a lot of the cars that were taking over the VW shows: Rabbits, Jettas and Golfs. Combine the water cooled VWs and the Euro custom and race look with the Japanese and American lowriders (that ironically were called "euros"), and the sport compact crowd that had been racing, and a new trend at the end of the ['80s was born. Race replicas in the car show circuit. Those that had been building custom VWs had been looking to the European models we couln't get here, and those that had been building Japanese cars looked to the Japanese market supercars that weren't available here.
In Japan, for years, the race replica market had been big. Motorcycles were teh primary thrust of it, with people riding 50 and 125cc sportbikes made up to look like grand prix racers. They'd ride around in packs showing off. Asians in the US, to show "asian pride" (more accurately, "AzYn PrYd") brought over everything Japanese, from clothing trends to motorcycles and cars. In teh late '80s, teh cars available from Japan had gotten very capable, and chock full of every bit of tech that was possible. At the same time, only a handful of American cars were worth mentioning, and even the "fast" ones were poorly built. Both Japanese and Euro fans started being extremely vocally anti-American car. But it was still local pockets.
About that time, the F40 became a poster car, and the Japanese came out with cars like teh Supra Turbo, with it's huge factory wing. Suddenly, the sport compact magazines carried ads filled with fiberglass and ABS wings for every kind of car you could imagine. Everyone wanted that huge turbo car exhaust, and the race and rally airdams and side skirts became avaialbel everywhere. Every litle asian car owner was tryin gto build their own fake Supra Turbo. Honda came out with their VTEC engine tech and all the little AzYn PrYd" wannabes had to put those emblems on their cars and run around saying how great they were. The era of the riceboy had begun (this would be about '91-92). Before that, you simply never saw cars like these:
The wings, the big turbo exhaust, etc, simply didn't exist in the aftermarket. This was a huge change from cars like this:
Those were called Rice Rockets from day one. But the new trend was Riceboy and Ricers, a completely different thing. Ricers were primarily poseurs and fakes with a serious attitude problem.
Fast forward a couple years, and the rise of the internet and the rapid dissemination of information from coast to coast. AzYn PrYd was infiltrating every automotive message board, dissing on any American car, and occasionally Euro cars. Everyone across the country could see the cars start showing up in their towns. At the same time, cars like the Camaro Ss were arriving from the factory able to handle and accellerate better than musclecars had in the past, and the aftermarket for them and Mustangs had made it cheap and easy to make those cars very quick indeed. As the Riceboy infiltrated the web, the backlash was huge. While Bryan had identified it in '91-92 and gave it the name that stuck, his site set the tone for all that followed: RiceCop.com, AntiRice.com, and many, many more (many of them started by members of his original site).
Riceboy and Ricers was the term given to people who modded their cars in an effort to look like their cars were race cars and fast cars. usually using fake parts (like fake intercoolers and BOVs on cars with no turbos), stickers for parts they didn't have or weren't even avaialble for their cars (like Mugen windshield banners on Camrys), or trying to make their base level cars look liek the fast models (like VTEC, Type R, and SiR stickers on Civic DXs and non-VTEC models)
Using parts from other cars on your car is customizing, or using the STYLE of other cars on your car. It's traditional and has been around forever. Lambo doors look unique when opened, but don't change the look of the car in normal use, nor does anyone do it to make their car look faster. But things like this are a whole different story: