Ill-natured - drift sideways on couch (7)
I believe the answer is:
crabbed
'ill-natured' is the definition.
(similar in meaning)
'drift sideways on couch' is the wordplay.
'drift sideways' becomes 'crab' (to move like a crab).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'couch' becomes 'bed' (I've seen this before).
'crab'+'bed'='CRABBED'
(Other definitions for crabbed that I've seen before include "Surly" , "Bad-tempered like crustacean" , "being hard to decipher" , "morose" , "(Of writing) hard to read" .)