Guagua is a fun and unique word that means "bus" in some Caribbean Spanish dialects, particularly in Puerto Rico and Cuba. It's a great example of regional vocabulary that makes learning Spanish so interesting.
In the song, the lyric "Me dejó la guagua, ¿Y qué?" translates to "The bus left me, so what?" It highlights a carefree attitude towards minor inconveniences, using a charming, less common word for a common mode of transport.
Martox and Lena Dardelet build a whole song out of a bad morning. The power is out, the alarm never went off, the bus has gone without you, and then it starts raining. Each one gets the same two word shrug: "Se nos fue la luz, ¿Y qué?" (the power went out, so what?), "Me dejó la guagua, ¿Y qué?" (the bus left without me, so what?). The repairs are just as small. Sugar in the coffee from "Un cafecito por la mañana" (a little coffee in the morning), and a candle when the lights die in "Prendo una velita, ¿Y qué?" (I light a little candle, so what?).
Halfway through it stops shrugging and makes an argument. "Todo lo que sube vuelve a bajar" (everything that goes up comes back down) would read like a fridge magnet anywhere else, but the track has earned it by spending two minutes on a power cut first. Then it narrows down to two people and a beach: "El mar, el sol, nada más somos tú y yo" (the sea, the sun, it's just you and me). One word worth keeping from it: "guagua" is what a bus is called in the Dominican Republic, where both of these artists work.