Irritable

a.
  1. Capable of being irritated.
  2. Very susceptible of anger or passion; easily inflamed or exasperated; as, an irritable temper.
  3. (Physiol.) Endowed with irritability; susceptible of irritation; capable of being excited to action by the application of certain stimuli.
  4. (Med.) Susceptible of irritation; unduly sensitive to irritants or stimuli. See Irritation, n., 3.