Teacher in a flap upended coffee-maker (7)
I believe the answer is:
barista
'coffee-maker' is the definition.
(term for a cafe worker)
'teacher in a flap upended' is the wordplay.
'teacher' becomes 'sir' (way of addressing a male teacher).
'in' is an insertion indicator.
'flap' becomes 'tab' (both can mean a small piece of material).
'upended' says the letters should be written backwards (in a down clue, letters go up).
'a'+'tab'='atab'
'sir' put within 'atab' is 'atsirab'.
'atsirab' in reverse letter order is 'BARISTA'.
(Other definitions for barista that I've seen before include "person serving drinks" , "Coffee maker?" , "Coffee servitor" , "Starbucks employee" , "Coffee bar server" .)