A phrase used instead of sweet for the sake of humour. Sometimes, this is said in an ironic manner as sweet dreams would be a nightmare for a diabetic patient.
Person 1: "Aight, imma head out now, bois"
Person 2: "Haha, I guess, hope you have salty dreams!"
Person 1: "Haha, wait what?
A nineyear old that breaks the sound barrier when they die in Fortnite.
Nine year old, Nine year old, here comes the Salty Nine Year Old, screams so loud, break the sound barrier, watch out! Here comes the Salty Nine Year old.