If you describe someone as excitable, you mean that they behave in a rather nervous way and become excited very easily. Mary sat beside Elaine, who today seemed excitable + excitability ex·cit·abil·ity She has always been inclined to excitability. becoming excited too easily
The property manifested by living organisms, and the elements and tissues of which they are constituted, of responding to the action of stimulants; irritability; as, nervous excitability