Rihanna -- Back in the Passenger Seat ... With Chris Brown

And just like that ... Rihanna's back where it all started ... Chris Brown's passenger seat.

The on-again couple relived their past earlier today in L.A., where they picked up some refreshments -- including an Icee -- at a gas station convenience store.

You'll recall, Rihanna was riding shotgun back in 2009 when CB unleashed a ferocious beatdown on her face -- but today, she was nothing but smiles.

Oh yeah, that red sweatshirt she's wearing is Chris' clothing line -- Black Pyramid.

Hope Part 2 works out better.