Trendy drink I had? Flavourless (7)
I believe the answer is:
insipid
'flavourless' is the definition.
('insipid' can be a synonym of 'flavourless')
'trendy drink i had?' is the wordplay.
'trendy' becomes 'in'.
'drink' becomes 'sip' (I've seen this before).
'i had?' becomes 'id' (I'd).
'in'+'sip'+'id'='INSIPID'
(Other definitions for insipid that I've seen before include "Jejune" , "flat" , "dry" , "Tasteless" , "Lacking taste or flavour" .)