07/23/2012 at 06:00 AM EDT
wasn't about to let a stormy day in New York City ruin her fun.
The What to Expect When You're Expecting
star braved the rain on Wednesday when she headed to Chelsea Market for the Blackberry PlayBook launch, hosted by Voli light vodka.
Diaz, who popped in with an unidentifiable male and his two kids, "took her shirt off at one point to wring out her drenched top," an onlooker tells PEOPLE. "For a minute, she was only wearing a sports bra."
The actress, who put her top back on once it was drier, "stayed for a little bit and sipped on a vodka drink," the source says. "Whomever the male was seemed quite close to her." – Dahvi Shira