It's "rice" because it's asian; it's a derogatory term used towards people and their cars. When I was younger, this term was used against asian drivers and their asian cars - and it was not a compliment.

Looking at Urban Dictionary I see no mention of this anti-asian side of it, but it was there when I was growing up. Maybe others can chime in with their experience, I imagine it wasn't the same everywhere.

Not implying the people using it here are being racist, I don't think they are aware of what I'm recalling here.