Justin Bieber: I'll Take Pics With Fans ... If They're in Diapers

Justin Bieber was so enamored with an adorable baby while eating sushi in Malibu ... he put a temporary kibosh on his strict no picture policy.

JB was at Nobu on Monday when he passed by 6-month-old Nikki eating lunch with her family.

We're told Justin stopped and said, "Aww, who is this little baby she's so cute," and immediately asked to hold her. He asked if she was a fan and gave her a kiss on the cheek.

Justin even came back after lunch to see if Nikki missed him.

He also trolled his fans by posting a pic with Nikki and calling her his daughter.