Rihanna --25th Birthday with Chris Brown ... and TINY BIKINI

Rihanna celebrated her 25th birthday in Hawaii yesterday ... with on-again boyfriend Chris Brownby her side.

The singer posted a shot of the two of them together on her Instagram account, showing her with a huge smile on her face as she sits on his lap. "Pour it up pour it up! #birthdaybehavior," she posted along with the pic.

She also posted shots from her party, showing them eating cake and celebrating together -- see those photos in the gallery above.Earlier in the day, the couple was also seen walking along the beach hand-in-hand.


It's pretty clear that it's "Game On" with these two, who also attended the Gram-my Awards together last week. 

It wasn't all one-on-one time with her controversial ex though, as her BFF Melissa Forde also posted some shots of RiRi's birthday celebration as well -- including this one, which came with the message "Wasted."

Will you ever get used to seeing her back with Chris, considering their violent history together? Sound off below!

Chris B made his way across the Pacific to meet up with Ri Ri in Hawaii, where she and her crew have been pouring it up and smoking it up for her b-day.  And it looks like a crazy amount of fun..