Extremely tacky company working for fat cat (6)
I believe the answer is:
tycoon
'fat cat' is the definition.
(both can mean a rich person)
'extremely tacky company working' is the wordplay.
'extremely' means to remove the middle letters (only the extremes of the word are used).
'company' becomes 'co' (abbreviation).
'working' becomes 'on' (on can mean working or activated).
'tacky' with its centre taken out is 'ty'.
'ty'+'co'+'on'='TYCOON'
'for' acts as a link.
(Other definitions for tycoon that I've seen before include "Big noise" , "Entrepreneur" , "Big cheese in business" , "See 2" , "One very wealthy" .)