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Similar to a birthday, except instead of celebrating the day a man was born, he celebrates the day in which his penis reached its maximum girth.
Hey ladies!! Today is my girthday, and i was hoping you'd celebrate with me by letting me go deep inside! Whaddaya say?
by MikeyB1980 January 16, 2014
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Girth Day occurs every May 1. It is a day to honor those among us that are Girthier than the average man. Examples of honorees include: Arnold Schwarzenegger, Jean Baptista, and Ron Jeremy.
Happy Girth Day!
by jmn3813 April 30, 2011
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The day by which you loose ur virginity.

derived from the words girth and birthday...girth being the thinkness of the penis
jordan: happy girthday!
andrew: cheers mate, i cant believe its been 9 years now!!
happy birthday penis
by <<*ROoOo*>> August 14, 2008
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The day that your dick reaches maximum circumference, or girth
Ben: Hey dude when was your girthday?

Drew: Man my girthday was September 4th of 1969, the good ol' days.
by Literally_Awful February 19, 2015
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