Pianinho is the diminutive form of piano, meaning "little piano". While it literally refers to a small piano, in the context of Brazilian funk and baile funk, it's a slang term for a specific dance move.
In "Vai Dar Ruim," the phrase "no passinho do pianinho" (in the little piano step) refers to a popular dance step where dancers mimic playing a piano with their fingers while moving their bodies. It's a playful and iconic move within the genre, making the word both unique and culturally relevant to the song's style.
"Vai Dar Ruim" is pure passinho energy, a call-and-response funk track built for the dance floor and not the headphones. Dream Team do Passinho spend most of it just repeating commands: "Vai dançando (vai dançando!)" [Keep dancing (keep dancing!)] and "Vai neguinho (vai neguinho!)" [Go on, dude (go on, dude!)], the sort of chant a DJ throws at a crowd to keep a passinho circle moving.
Between the chants there is a loose scene. The singer rounds up "as pretinhas do meu bonde" [the girls from my crew], dressed "De salto e divando" [in heels and being a diva], and asks someone to "passa a visão qual é a do baile" [tell me what's up with the party]. The title line, "vai dar ruim" [it's gonna be bad], reads less like a warning and more like a boast: things are about to get wild doing "No passinho do pianinho" [in the pianinho step], the move that gives the song its name.