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1. Exaggeration of the word 'Happy'

2. Often used in a birthday wish

3. characterized by or indicative of pleasure, contentment, or joy.
"Have a happy flappy birthday!"

Can be used as a 'messy birthday wish' as in: "Hope you have a happy flappy birthday. Lots of slobbery kisses, Mr. X"
by BlankoBP May 26, 2011