Miley Manhandles Boytoy

So we showed you Miley Cyrus' glotta-see-this moment with her model BF at a fashion show yesterday.

Turns out that the tongue-slippage didn't necessarily stop there: the New York Post says MiCy and Justin Gaston "were all over each other backstage" at the Christian Audigier show. In fact, they might've skipped the afterparty ... for "a party of their own."

Miley's rep says the "whole sleeping-over thing never happened" because mom Leticia put the kibosh on it.