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.
Spanish rapper C. Tangana is utterly wrecked in "Mala Mujer", and he blames one person: an ex whose memory literally claws at him. The hook is wonderfully dramatic, claiming her uñas de gel (gel nails) left actual cicatrices por todo mi cuerpo (scars all over my body). Instead of moving on with dignity, he describes himself roaming the streets like a lost dog caught in her scent, drinking too much, and spiraling into a mess: bailo borracho, perdido, desesperado (I dance drunk, lost, desperate).
He rewinds to the club night where his ruin started. While getting ready in the DJ booth, he spotted her mesmerized on the dance floor while a track by Spanish urban artist Dellafuente played in the background. He knew right then he should have bolted, but he could not look away. By the end, he calls her a straight-up thief (ladrona) who wiped him out completely. In Spain, pasta is everyday slang for cash or dough, and he complains that she stole his heart, his pride, his peace, and mi pasta (my money). While he sits around crying about it, she is still out there dancing without a care.