when a guy lubes down the line from a girls mouth, between her breasts and up to her crotch. she stands on her head and the guy drops a log on her vagina, the lube will allow it to slip directly into her mouth, thus creating a chocolate fall.
Bobby lubed a line from Suzy's mouth, between her breasts, between her abs, all the way to her clitorus. She propped herself up on the back of her neck with her vagina pointing upwards toward the ceiling with a slight angle to let the shit slide. Bobby dropped a turd at the top of her vagina, and that log slid right into her mouth, boy that was a good chocolate fall!
When someone stands on another's shoulders and they both take a dump (preferably diarrhea) at the same time, thus producing a cascade-like effect.
Last time I had mexican for dinner, me and Linda got drunk and made some chocolate falls on Steve's garden. It was quite heart (and back) warming.