Mamacita literally means "little mama" but is commonly used as a term of endearment, often with a flirtatious or suggestive connotation, similar to "babe" or "hot mama" in English.
In "Menos De Ti," Greeicy uses this word to reject a past lover's attempts to label her. She declares, "Que no diga que yo soy tu mamacita" (Don't say that I'm your mamacita), asserting her independence and refusing to be defined by him. This makes it an interesting and culturally relevant word to feature.
Greeicy is done, and she wants you to know exactly how done. She opens with "Tu cuerpo era mi vitamina" (your body used to be my vitamin), past tense, no apology, and by the second line she's already checked out: "Y ya no me haces sentir nada" (and you don't make me feel anything anymore).
The real hook isn't the chorus's kiss-off line, it's the twist buried inside it: "Y me encanta que ya no me encantes" (and I love that you no longer enchant me). She isn't pretending the spell broke by accident. She's savoring it. When she repeats "Y mucho menos de ti" (and much less of you) five times in a row, it stops sounding like a lyric and starts sounding like a sentence she's rehearsed for months. By the bridge she's calling him "pobre diablo" (poor devil) and stacking three flat verdicts in one line: "no me tiene, no me entretiene, no me conviene" (you don't have me, you don't entertain me, you don't suit me).