Anyone who puts anything on their car for either incorrect reasons, or just for the sake of it looking like something that's useful on some other type of car. Also, modifying a car that truly has no performance potential just because it's what they happen to have in their garage could also make a person a ricer.
examples....
A ricer would put a $20 ebay muffler on their chevy cavalier and insist it added 15-20hp.
A non-ricer might add the same muffler and admit that it just made the car louder, or maybe added 1 or 2 hp.
A ricer would buy a "turbonator" or an electric boat bilge fan to put in their intake to add power.
A non-ricer would laugh at that and save his money for a part that isn't advertised in an infomercial (or sold at a marina).
A ricer would buy a $15 bottle of octane booster and tell everyone it gave him the same thing as 115 octane race gas.
A non-ricer would buy a meth injection kit for his car or convert it to run on E85.
A ricer would put steel wheels on his drive wheels with tall sidewall all season tires to use on the drag strip, and drive the car like this all the time to look cool.
A non-ricer would put steel wheels on his drive wheels with drag slicks to use on the drag strip, and take them off before he drives home.
A ricer would spend $4000 on a turbo kit for his car that adds 50hp, and then put 500 pounds of 20" chrome wheels, neon lights, LED exhaust tips, subwoofers, and fish tanks in the car that completely negate any performance gained by the turbo.
A non-ricer would build his turbo kit himself after researching for months and buy forged wheels and a lightweight flywheel to make up for the 40 pounds he added by putting a 12" sub in the trunk (and take the sub out at the track).