1. Short for "Schizophrenic" as in "Paranoid Schizophrenic". Which is a severe mental disorder often confused with "Mutiple Personality Sydrome".
2. Someone with wildly diverse personality traits that manifests themselves in a less than sane manner.
That bitch is a schizo. One minute she's a Sunday school girl, the next minute she's crack whore that would make a sailor blush.