Heidi's Alleged Sex Tape Partner -- Naked Sunbather
8/23/2010 9:00 AM PDT
Heidi's Alleged Sex Tape Partner -- Naked Sunbather
Playboy Playmate
Karissa Shannon -- the star of an alleged girl-on-girl sex tape with
Heidi Montag -- showed off the goods in Vegas this weekend ... during a quasi-naked sunbathing session.

As we previously reported, Karissa doesn't deny that a tape exists ... but she's not convinced that
Spencer Pratt is actually in possession of it.