The adjective form of testicle is testicular. The phrase should be "testicular fortitude".
I just met a guy who can't tell the difference between a noun and an adjective. It takes a lot of testicular fortitude to display your ignorance in public like that.
by My dixie wrecked November 25, 2003
means having balls, bravery, courage
if ya wanna win, u bettah reach down and grab for sum testicle fortitude
by Inflame November 23, 2003