when somebody is so horny it's sad, looking for a partner that they sacrifice anything to get one, or they're that desperate to do something,
Justin: "bro, Micheal is so down bad he can't go one second without simping over a girl"
Aubrey: "Kate so down bad for a bag of Skittles."
Luis: "bro i'm so down bad for some coochie, if you're a busty one then dm now."
down bad does not mean "h0rny" it just means somebody did something you didn't like or something that upset you
Boy 1: Ms.Jones gave me a detention
Boy 2: Dang she did that down bad
dude: looks at girl
tells friend: sheesh that girl is down bad
Extremely in love with someone, would do anything for that person. Including(but not limited to) human experimentation.