a complex sexual practice, usually occurring between two men, in which one partner penetrates the other partner from behind ("doggy style"), and in the moment before ejaculation, spits on the receiving partner's back to trick him into believing he has ejaculated already. When the receiving partner turns around, the penetrating partner then ejaculates into the receiving partner's face.
The phrase is largely used among members of the gay community and likely originated in San Francisco. The provenance of the "Chinatown" in the phrase is thought to hail from the common practice of Chinatown's residents to spit loudly on the street. There are several conflicting opinions about the provenance of the "Rodney" in the phrase, most attributing it to any one of several promiscuous gay men named Rodney presiding or socializing in San Francisco's famously homosexual Castro Street area.
I'm gonna give Ron Jeremy a mean chinatown rodney!