Customers, cold and silent, getting upset (7)
I believe the answer is:
clients
'customers' is the definition.
('client' can be a synonym of 'customer')
'cold and silent getting upset' is the wordplay.
'cold' becomes 'C' (eg on taps).
'and' means one lot of letters go next to another.
'getting upset' indicates anagramming the letters.
'silent' is an anagram of 'lients'.
'c'+'lients'='CLIENTS'
(Other definitions for clients that I've seen before include "Customers of the professions" , "Consumers" , "Stencil (anag)" .)