Shows off pens, perhaps 1000 collected (6)
I believe the answer is:
swanks
'shows off' is the definition.
('swank' can be a synonym of 'show off')
'pens perhaps 1000 collected' is the wordplay.
'pens perhaps' becomes 'swans' (pen can mean a female swan).
'1000' becomes 'k' (synonyms).
'collected' is an insertion indicator (inserted letters are collected by others).
'swans' enclosing 'k' is 'SWANKS'.
(Other definitions for swanks that I've seen before include "Behaves in boastful, ostentatious way" , "Informally, behaves with boastful show" .)