adj

• (informal, figuratively, of a person or behavior) Short-tempered and gruff but, sometimes, with a harmless or benign inner nature.
  "However kindly a friend may otherwise be, he soon turns crusty if asked to lend money."
• (informal) Of very low quality; crude visuals or harsh, granular sound.
  "The door opened with a crusty squeak that echoed in the silent room."

noun

• (chiefly British, informal) A tramp or homeless young person with poor cleanliness.
• (slang) Dried eye mucus.
  "Against the backdrop of muted stripes of color, Julieanne picked at her eyes’ crusties, and then combed her hair with the hand."
• (chiefly UK and Ireland, informal) A member of an urban subculture with roots in punk and grebo, characterized by antiestablishment attitudes and an unkempt appearance.
  "The Spirals are part of the crossover between the rave scene and the ‘crusty’ subculture—crusties being squat-dwelling anarcho-hippy-punk types named after their matted dreadlocks and post-apocalyptic garb."