Top Definition
The emotion evoked when someone says or does something which is not merely 'yay,' but significantly greater 'yay' than normal. Also known as the superlative form of yay.
Girl: "Guess what?"
Guy: "What?"
Girl: *loving kiss* "I love you"
Guy: "Yaytasticness! I love you too."
by xkcdreader August 01, 2010

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