Feeble Hollywood movie: but it’s hard to shake off! (6)
I believe the answer is:
limpet
'it's hard to shake off' is the definition.
(limpets cling to rocks)
'feeble hollywood movie' is the wordplay.
'feeble' becomes 'limp' (I've seen this before).
'hollywood movie' becomes 'ET' (E.T. the Extra-Terrestrial).
'limp'+'et'='LIMPET'
'but' acts as a link.
(Other definitions for limpet that I've seen before include "Shellfish that sticks to surface" , "Proverbially clingy mollusc" , "Shellfish; type of mine" , "Clingy person" , "It clings to rock surfaces" .)