He usually uses it in joyful exclamation about how something is SO yummy and juicy...I'm not sure if he thinks that juicy=yummy though. Examples include:
"Thank you for the banana, Mama!! It's SO juicy!" (hmmm on the instructions for my juicer it explicitly says not to try juicing 2 things: bananas and dried fruit)
"Mmmmmm Mmmmmm! This carrot is so juicy!"
"Thank you for the juice, Mama! It's so cold and juicy!!!" (I guess he's getting closer!)
He makes me laugh! :)