I dont really know the origins, but the first time I heard it was like 5 years ago when I bought my first car, a non turbo dsm, my friends would call it a rice rocket, i asked them why and they told me it had to do with it being a japanese car and them eating rice.

From then on, it became ricer, which is more of a derrogatory term, you DONT wanna be a ricer, a ricer is a wannabe racer.

Rice can also be things that 'make' your car look faster but doesnt, IE big a$$ wings, body kits, APC lights, etc etc.