When you are talking to someone and they don't happen to hear you or are spacing out, you say this phrase. It implies that they are like a tree and are impervious to their surroundings. Then, hopefully, they'll hear it and start paying attention.

I don't know if this phrase is used in English but I know it is used in Spanish. My Colombian friend used this when I didn't know she was talking to me. However, she said it in Spanish: "Feliz Dia del Arbol"
Person A: blahblahblah
Person B: *spacing out*
Person A: Happy tree day!
by Flora H January 8, 2006
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