### Clue: Irritable and sarcastic when starting direction switched (5)
### Answer: NARKY 
 ### Explanation: Definition: Irritable
 "sarky"(slang for "sarcastic") **with its 1st letter**(starting) "s"(abbrev. for "south",a direction) **changed to**(when … switched) "n"(abbrev. for "north", the opposite direction).