(n.) 1. one who lacks mental stability 2. a lack of mental stability, e.g. insanity 3. The portion of the skull enclosing the brain
1. "That braincase almost ran into me!" 2. "He must have a braincase if he's wearing those clothes." 3. In the car crash, Mikecracked his braincase, resulting in his death.
A brainraisin is reference to some stupid, irrational and underdog verbal or textual expression... just say something stupid; like this last paragraph defining BrainRaisins.