The bravest Frenchman is a tongue in cheek phrase used to represent the concept of a mutually exclusive enigma. The French are typically represented as the first to give up in a fight, fly the white flag & let someone else fight their battles for them. It is like saying, "who is the strongest weak man?"
Watching the first graders play a pee wee baseball game was like trying to figure out who is the bravest Frenchman.