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1.
a lie regarding one's penis size
Mike said he had a 9 inch dick...that is SUCH a phallacy...
by Whitty May 26, 2003
 
2.
Phallacy is the name of an amazing clothing company which offers magical color changing clothes.. That's right clothes that change color when you go outside. AMAZING MAGICAL

The word phallacy is a play on the word Fallacy as in a misleading argument or false argument.. Thus Phallacy's Clothing misleads many by having things appear on it..
Dick: Dude did your shirt just change color?

Jane: Yeah it's magic nig!

or

OMG YOUR SHIRT JUST HAD STUFF APPEAR ON IT !

DUH I bought this wonderful color changing shirt from phallacy lets go play in the sun and make it change...
by The Phallacy September 13, 2006
 
3.
A spurious statement regarding the size of one's penis.
He uttered an unforgivable phallacy last night. The sad thing is that it worked... She went to his room during the party. I can only imagine the look on her face after he dropped trou.
by HanTzu November 03, 2010