Rihanna -- CLOWNS TMZ Photog ... You Want Fries With That?

You know you're a super hot chick when you can call a guy "fat ass" ... and minutes later, have him eating out of the palm of your hand -- something Rihanna has perfected to a T.

RiRi was bailing from Toxic at Lure Saturday night when she grilled our camera guy -- pun intended -- about his love for greasy food.

The best part ... just minutes later she apologizes and our photog is once again smitten.