This can be used to define times when a guy does something that requires a great deal of nerve and skill, but he is truly lacking in skill and ends up hurt, humiliated, and/or dead. Alcohol is considered the main accelerant to this condition.
Roz looked down from the 58 foot cliff that overlooked the shallow, rock-filled lagoon. While diving to his imminent death, he knew that his balls were bigger than his brain.
Bobby “Why is that guy riding a motorcycle with no helmet at 130 mile per hour (209 Kilometers per hour)?”
Brandon “That’s because he has a bad case of Balls No Brains”
Bobby “damn! That guy just punched one of the robbers in the face, too bad he’s about to get shot.”
Brandon “That guys got a serious Balls No Brains way of thinking.”