A sleeper is the complete opposite of a ricer.
Ricer: "LOL, look at that 350Z. It suxxx. Mah Civic is better in EVERY WAY POSSIBLE."
Z Driver: "I see you're challenging me to a race."
Ricer: "Yo, imma show yo the real power of zis Civic. We race. And I shall win. I'm serious."
Z Driver: "Don't even try. I've got more important matters to attend to--"
Ricer: "YOU SHUT UP! WE'LL RACE, AND I'LL WIN, AND I KNOW IT."
-a little while later-
Ricer: "Goddamn it! YOU N00B! GET BACK HERE FOOL"
Z Driver: "No u."
(Z Driver drives away doing the "lol internet")