The true definition of "rice" is simple. When a person says that something or someone is "ricey" or what have you...he/she is saying "I have no life, I am a loser, I like to make fun of people, I wish I could get laid".
Truth be told though, it's a bash on all Japanese cars, modded or not, simpley because they are made by Japanese companies. But the ironic thing is that most of the people who call something ricey own imports....go figure.