The duo, who both star alongside Taylor Kitsch and Liam Neeson in the blockbuster, are currently in Australia, where they attended the film's premiere in Sydney last night (April 10).
Rihanna explained the origins of their stunt: "This journalist came into an interview of ours, I think in London, and he had a Rihanna T-shirt and Brooklyn said, 'I'm getting a Rihanna T-shirt'.
"I said, 'No we should get Pete Berg T-shirts'. So it was her idea and we ended up getting them printed and the whole cast has them. I cannot wait to see his face."
Attending the premiere last night (above), Rihanna opted for a black Stella McCartney jumpsuit, while Decker wore a floor-length J. Mendel dress.
Meanwhile, the duo also joined fellow cast members on a yacht yesterday, enjoying a trip around Sydney Harbour.
> Rihanna fights off aliens at sea in new 'Battleship' trailer - watch
Watch the trailer for Battleship below: