The kind of opposite of upchucking. When you vomit a bit, and you accidentally swallow it. Leaves nasty taste in your mouth, and it can often happen many times if you are hungover.
Guy 1: "Damn it, after that massive party I fucking downchucked like 8 times"
Guy 2: "That's nasty"
to vomit into someone's gaping vagina or anus
Jacob likes to downchuck into Michael. Michael loves it.