Person showing off difficult puzzle (5)
I believe the answer is:
poser
I believe this is a double definition.
'person showing off' is the first definition.
(a person who poses)
'difficult puzzle' is the second definition.
(I've seen this before)
(Other definitions for poser that I've seen before include "Puzzling question about ropes" , "Someone behaving so as to be noticed" , "Puzzling problem" , "Question; one trying to impress" , "Puzzling question for the model" .)