Bellaquera is a colloquial and somewhat vulgar term in some Spanish-speaking regions, particularly in the Caribbean, that refers to a state of intense sexual arousal or desire. It can be translated as "horniness" or "naughtiness" in a sexual context.
In the song, Standly uses it quite directly when he sings, "Qué bellaquera lo que hicimos aquella noche" (How horny/naughty what we did that night). It's a very explicit and raw word that immediately sets the tone for the song's themes of passion and sexual encounters, making it memorable and attention-grabbing.
The whole song happens behind the wheel. "En la carretera / Pensando en ti, en mi coche" ("On the road / Thinking about you, in my car") is the hook, and what Standly keeps replaying on the drive is one specific night: "Lo que hicimos aquella noche" ("What we did that night"). He describes her in the same vocabulary he uses for everything else he carries around — "Tiene el pelito negro como mi Glock" ("She has black hair like my Glock"), "Me relaja como un blunt" ("She relaxes me like a blunt"), "De a poco tú fuiste mi drogadicción" ("Little by little, you became my addiction").
In between the boasts he keeps stopping to ask something he does not know the answer to: "Y dime si somos o no somos" ("And tell me if we're a thing or not"), then "Vente pa' acá conmigo" ("Come over here with me") if "no te sientes amada" ("you don't feel loved"). He settles on a title for himself, "Tu flaite romántico" ("Your romantic flaite" — flaite is Chilean street slang for a guy from the rough end of town), and the rest of the verse is explicit about where the highway is heading. It ends the way it started, engine still running, on the ad-libs "Pa' las babies" and "El Standly".