when your penis shrinks after taking cocaine or speed
I got really bad billy willy last night. did you?
by polsky November 23, 2007
billy willy is when your dick is so small and unfunctional because the "whizz" (cockney rhyming slang) "billy whizz" = speed has done what it enevitably WILL do to your bulk of your manhood :D
"oh fuck love, i got billy willy"
by Jobie1 ;) October 24, 2004