An intensifier that follows an action verb to indicate that the action is or will be done to the utmost degree. Commonly heard in the phrases "beat (one's) brains out" and "blow (one's) brains out." I'm not going into that haunted house—the kids in there already are screaming their brains out! I'm worried that the captain of the football team will beat my brains out if he finds out that I'm secretly seeing his girlfriend.