his balls were bigger than his brain
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.