Heather goes behind boat, looking displeased (8)
I believe the answer is:
scowling
'looking displeased' is the definition.
(I've seen this before)
'heather goes behind boat' is the wordplay.
'heather' becomes 'ling' (synonyms).
'goes behind' says to put letters next to each other.
'boat' becomes 'scow' (scow is a kind of boat).
'ling' put after 'scow' is 'SCOWLING'.
(Other definitions for scowling that I've seen before include "Frowning with displeasure" , "Lowering" , "looking unhappy?" , "looking displeased" , "glowering" .)