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The morning on which a male wakes up and finds his cock to be much larger than the day before. Usually accompanied by fervent celebration, and parties (usually sex parties).
Todd: Dude my dick grew 1/2 an inch in girth last night!

Manuel: Congratulations man! Happy Girthday! Are you getting laid tonight?

Todd: You know it man!
by FuctButSects October 22, 2010
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