Descaro translates to "shamelessness" or "audacity." It's a strong word that conveys a sense of impudence or lack of shame.
In "Es Mentira," Christian Nodal uses descaro to describe the ex-lover's brazen attempt to return after causing so much pain. He sings, "Y ese llanto solo refleja el descaro de / Intentar de nuevo el burlarte aquí en mi cara," highlighting the audacity of their tears and their attempt to deceive him again. This word perfectly captures the singer's indignation and the ex-lover's lack of remorse.
Christian Nodal calls out an ex who shows up sounding repentant, and refuses to buy it. He opens almost graciously — "No te preocupes que no te guardo rencor" ("Don't worry, I don't hold a grudge against you") — before turning the knife: "Pero con la pena hoy te informo que pa' ti ya no hay amor" ("But sadly, today I have to tell you there's no love left for you"). The regret arrived too late, and he's not interested in reopening the door.
The title line does the real work. "Y es que sé que es mentira" ("And I know it's a lie") repeats through the chorus, aimed at every tear and promise she brings back to him now that her own plans fell apart. By the last line — "Yo sé que no vales nada" ("I know you're worth nothing") — the verdict is final: this isn't heartbreak anymore, it's a door closing on someone he's already seen through.