A schmuck of a model, most often a fashion model. She's conceited, pushy, lacks an awareness for the meaning of "punctual", often is a no-show, and usually demands more money than she's worth. Other girls may refer to her as "skinny bitch" or "model whore", even though the latter is not entirely accurate at times (but most often it is).
A schmodel's diet consists mainly of vodka and cigarettes.
A schmodel may also be male. But male fashion models are harassed enough as it is, so the above description is for the female variety of schmodels. However, the likelihood of a male schmodel being referred to as "skinny bitch" and "model whore" is just as great as that for the female schmodel.
Photographer: "First she showed up three hours late for the shoot, and then that damn schmodel demanded I get her an iced chai latte with exactly four ice cubes (no more, no less) before she'd even sit down for makeup!"