this is a term of endearment used for couples crazy in love that are way past the early days of whispering sweet nothings like 'you're beautiful' or 'you smell nice.' If you tell your beloved they are a stinky baby then they know you really love them.

a stinky baby is simply someone in your friend group who either acts immaturely when it comes to din dinns or beddy baws, or someone who always complains.

You should always react to a stinky baby by saying "Waaaaaaaa" to mock them for being a stinky baby