I had to Google it, but apparently it comes from cars, where a riced car has stripes and spoilers and such to make it look like a race car.

One source claimed rice was race inspired custum e-forgot, the other did claim a link with asian street racing.

I expect that r.i.c.e. was overfit. Asian imports are called riceburners, ostensibly because asian cultures consume a lot of rice. I guess it could be contrived as racist, but it's relatively harmless in the scope of things...

I'm speculating further: but the imports were cheap and had a thriving aftermarket of bolt-on parts e.g. body and turbo kits. The low barrier of entry afforded opportunities for anybody to play. Ricing was probably a perjorative issued by domestic enthusiasts that was adopted ironically by Asian import enthusiasts. If you can imagine there was a lot of diversity, people who would bolt up body kits to clapped out Civics to people that would push 700hp with extensively tuned cars with no adornments. I think in particular ricing was the more aesthetically motivated of the crowd.

This was later adopted by computer enthusiasts that like to add embelishments to their desktops, things like rainmeter/rocketdock and Windows/Linux skins and etc...