小萌孙子爷爷在此
[xiăo méng sūn zi yé yé zài cĭ]
This translates to 'The little cute great-grandchild, grandparent is here.' It implies a playful role-reversal with a humorous twist, suggesting that the user has wisdom like a grandparent but is also approachable, charmingly childlike and adorable ('small and sprightly'), combining both generations' qualities humorously in one person.