Rihanna Takes Shots with Friends at Beach Bar in Barbados

Rihanna's getting rowdy down in the Caribbean ... downing shots with some friends at a beach bar in Barbados -- and, lifting a glass to her one-year-old son.

The singer-songwriter hit Thunder Bay Beach Bar on the small island country ... pulling up with a trio of friends to the spot this weekend and ordering tall shots of what looks like tequila, limes at the ready of course.

The four ladies pose for a pic before RiRi tells everyone to put their glasses in the air ... all while a worker at the bar films.

Rihanna asks the worker for her name, and she responds it's Rose -- a name that gets Rihanna's eyes to light up since it's her son Riot's middle name.

The group then has to raise a glass to her infant son -- born just over one year ago -- and, while you don't see Rihanna actually put the glass to her lips, it's pretty clear she's ready to down a drink.

BTW ... Rihanna asks if Rose can drink on the job -- and, when Rose says yes, tells her they need to take a shot together.

Just Rihanna in the clip BTW ... no A$AP Rocky or the kids joining her on this late-night excursion -- even though we know she's in Barbados with them.

Remember, last week photogs captured Rihanna and Rocky going for a quick dip with their boys. Cute family photos ... but, looks like Rihanna needed to let off steam on vacay too.