Heartless lad grabs single bunk (7)
I believe the answer is:
baloney
'bunk' is the definition.
(I've seen this in another clue)
'heartless lad grabs single' is the wordplay.
'heartless lad' becomes 'bay' (I can't justify this - if you can you should give a lot more credence to this answer).
'grabs' indicates putting letters inside.
'single' becomes 'lone' (synonyms).
'bay' enclosing 'lone' is 'BALONEY'.
Can you help me to learn more?
(Other definitions for baloney that I've seen before include "Tripe < , smoked sausage" , "foolish talk!" , "Tosh" , "rhubarb" , "Nonsense; lean yob (anag)" .)