Mila Kunis once delivered quite the inadvertent shock to her UPS driver.

The star of A Bad Moms Christmas opened up to PEOPLE for this week’s issue about an incident shortly following the birth of now-11-month-old son Dimitri Portwood, when she’d left her front door unlocked.

“My UPS guy is really sweet, and I’ve had him for years, and he always [just] drops off the package, but you can see him through the glass window,” she tells PEOPLE. “At one point, I was just shirtless, because I was hot. I was just with my baby, and I was three days postpartum, so it still was like [I was] pregnant.”

“I was just like, ‘Hey.’ Didn’t even think about it, naked, skin-to-skin with my baby,” recalls the actress, 34. “And he just puts the package down and looks up. And I was like … I didn’t even care.”

Kunis admits she “wasn’t really embarrassed” about the slip and “felt more bad for the UPS guy” than herself. “I was like, ‘This is not nearly what you thought you were walking into,’ ” she jokes.

“I think he may have been like, ‘Oh, that’s what they look like?’ You know, a nursing breast and a [non-nursing] breast. It’s just two very different boobs.” [Source]