Genteel euphemism for fabled non-traditional sexual act akin to "golden showers"; fetish of humiliation and self-abasement; in the act, one's lover/servicer squats and defecates onto one's face or chest while one is lying on floor or bed. The "chocolate" refers to fecal matter, while the "drop" replies to the satisfying plunk upon its arrival on face or chest. Some like to receive, while others strongly prefer to give.
Exchange overheard in heterosexual-themed bar, Warm Valley, ND, July 2006:
Stunned: "Whoa. I thought I knew what she meant when she said she wasn't into 'vanilla' sex."
Friend: "Yeah. Mmm-hmm (laughs lightly). I like that kinky shit too. Tie-me-up, tie-me-down. Let's go. All that shit."
Stunned: "Yeah, well, then she positioned herself, like squatting, like she was going to shit right on my chest."
Friend: "What the fuck?!?"
Stunned: "Yeah, it's like she called it 'the chocolate drop.' I was already tied up and she said I was gonna like it. It was way messed up."
Friend: "Whoa. What happened?"
Stunned: "Dude, I loved that shit. So fresh and so clean clean."