Evaporas comes from the verb evaporar, meaning "to evaporate." It's an interesting and somewhat dramatic word to describe someone's departure.
In "Peligrosa," the singer uses this word to vividly portray how the person he's singing about disappears suddenly and mysteriously, like a ghost. He sings, "Y te evaporas en la oscuridad sin decir nada" (And you evaporate in the darkness without saying anything), emphasizing the abrupt and elusive nature of her leaving.
Mana's "Peligrosa" is all about that intense, frustrating feeling when you're completely smitten with someone who's playing hard to get. Our singer is absolutely burning up with desire, saying things like "Estoy ardiendo en el sofá" [I'm burning on the sofa] and "Me tienes ardiendo en tus labios" [You have me burning on your lips]. He's clearly head over heels, but this person keeps disappearing, leaving him confused and a little crazy.
She's described as "tan peligrosa" [so dangerous] because she's got this power over him. She comes and goes "como un fantasma" [like a ghost], heating things up only to vanish without a word. He's begging her to stop playing games, insisting he won't hurt her, and he can read her true feelings in her eyes and kisses. He doesn't want to be just a pastime, he wants something real, but she's constantly leaving him wondering, "Mujer no se que diablos tienes tú, me estas volviendo loco" [Woman, I don't know what the devil you have, you're driving me crazy].