"Step Up 3D" star Sharni Vinson showed off her alarmingly slender bikini body on the beach in Sydney this weekend.
The 28-year-old -- who is currently dating "Twilight" muscleman Kellan Lutz -- could really use a cheeseburger about now.
So, we gotta ask ...
'Step Up 3D' Chick
Skin & Bones on the Beach
12/19/2011 4:00 AM PST BY TMZ STAFF
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