Ruina translates to "ruin" or "downfall". It's a powerful and dramatic word you don't hear every day, perfect for describing a complete disaster.
In this song, C. Tangana uses ruina to express total devastation. He sings, "Tú lo que eres es una ladrona / Que me has llevado a la ruina" (What you are is a thief / Who has brought me to ruin), blaming the "mala mujer" for destroying his heart, finances, and peace.
C. Tangana is completely down bad in this song, and he wants everyone to know it. He’s been wrecked by a relationship with a woman he calls a “Mala mujer” [Bad woman], and he’s not subtle about the damage. He says she’s left him with physical marks: “Me han dejado cicatrices por todo mi cuerpo / Tus uñas de gel” [Your gel nails have left scars all over my body]. Now that she's gone, he’s just trying to cope by getting wasted, telling us he wants to “perder el sentido / Y bailo borracho, perdido, desesperado” [lose my senses / And I dance drunk, lost, desperate].
He then flashes back to the moment he first saw her. He was in the DJ booth getting ready for his show when he spotted her dancing. He knew right then he should have stayed away, admitting, “Debí correr lejos de allí” [I should have run far away from there]. But he couldn't help himself. The song ends with a blunt list of everything she took from him, calling her a “ladrona” [thief] who stole his “corazón / Mi orgullo, mi pasta, mi paz, mi vida” [heart / my pride, my cash, my peace, my life]. It’s a total melodrama about being obsessed with someone who was bad news from the start.