Some wear ties, trendy, most pretentious? (7)
I believe the answer is:
artiest
'most pretentious?' is the definition.
('arty' can be similar in meaning to 'pretentious')
'some wear ties trendy' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'ARTIEST' is hidden in the letters of 'wear ties trendy'.
(Other definitions for artiest that I've seen before include "Most pretentiously aesthetic" , "Most pretentious" .)