Complete rubbish? Put hand over mouth! (8)
I believe the answer is:
claptrap
'complete rubbish?' is the definition.
'put hand over mouth' is the wordplay.
'put hand over' becomes 'clap' (I can't explain this - if you can you should believe this answer much more).
'mouth' becomes 'trap' (informal term for mouth).
'clap'+'trap'='CLAPTRAP'
(Other definitions for claptrap that I've seen before include "Utter rubbish" , "Pretentious talk or nonsense" , "Pretentious rot" , "moonshine" , "Tripe" .)