Being careless, knocks orange juice over disheartened engineer's sandwiches (6,4)
I believe the answer is:
sloppy joes
'sandwiches' is the definition.
(Sloppy Joe is an example)
'being careless knocks orange juice over disheartened engineer's' is the wordplay.
'being careless' becomes 'sloppy' ('sloppy' can be a synonym of 'careless').
'knocks' is a reversal indicator (I've seen 'knocking' mean this).
'orange juice' becomes 'oj' (abbreviation).
'over' means one lot of letters go next to another.
'disheartened' suggests removing the centre (the middle or heart is removed).
'engineers' with its middle removed is 'es'.
'oj' backwards is 'jo'.
'sloppy'+'jo'+'es'='SLOPPY JOES'
(Other definitions for sloppy joes that I've seen before include "Loose sweaters" , "Saucy hamburgers" , "tops!" .)