brittle

(noun): A confection of caramelized sugar and nuts.
(noun): Anything resembling this confection, such as flapjack, a cereal bar, etc.
(adjective): Inflexible, liable to break or snap easily under stress or pressure.
(adjective): Not physically tough or tenacious; apt to break or crumble when bending.
(adjective): Said of rocks and minerals with a conchoidal fracture; capable of being knapped or flaked.
(adjective): Emotionally fragile, easily offended.
(adjective): Diabetes that is characterized by dramatic swings in blood sugar level.

As a child, my favorite candy was peanut brittle.
A diamond is hard but brittle.
Shortbread is my favorite cold pastry, yet being so brittle it crumbles easily, and a lot goes to waste.
What a brittle personality! A little misunderstanding and he's an emotional wreck.