Stupid that hotel do only flipping sandwiches! (6)
I believe the answer is:
noodle
'stupid' is the definition.
(both can mean a stupid person)
'hotel do only flipping sandwiches' is the wordplay.
'sandwiches' indicates a hidden word (the solution is sandwiched in by the clue).
'flipping' shows that the letters should be reversed in order.
'eldoon' is hidden in the letters of 'hotel do only'.
'eldoon' backwards is 'NOODLE'.
'that' acts as a link.
(Other definitions for noodle that I've seen before include "In slang, a foolish person or just the head" , "See silly person" , "Thin strand of pasta" , "bit of pasta" , "Blockhead" .)