1982, acronym from "young urban professional," ousting competition from yumpie (1984), from "young upward-mobile professional," and yap (1984), from "young aspiring professional." The word was felt as an insult by 1985.
An exclamation of pleasure, esp of sensual delight (1878+)
Something sweet or pleasant, esp to eat (1889+)
[perhaps fr a locution used with children, hence contextually as well as phonetically related to tummy or tum-tum]