Natural juices produced by the human body, especially those belonging to the genitalia hence "from under" juice
See also: FromUndercheese
Dang girl you got some find "Fromunderjuice".
My thighs are so slippery and hot my "Fromunderjuice" is flowing for you tonight baby.
Mmm tastes like "Fromunderjuice"
That of which consist of pussy juice. Flavor depends om persons health and hygiene.
Her fromunderjuice taste sweet.
Oh snap! Your fromunderjuice is nasty bitch. Go get yourself clean.