Unpleasant in Monaghan as Tyrone (5)
I believe the answer is:
nasty
'unpleasant' is the definition.
(nasty can mean unpleasant or horrible)
'in monaghan as tyrone' is the wordplay.
'in' indicates the answer is hidden within the clue.
'NASTY' is hidden within 'monaghan as tyrone'.
(Other definitions for nasty that I've seen before include "Foul" , "Awful" , "One who sees the future" , "Not nice" , "grave" .)