It's pitiful when father gets the twitch (8)
I believe the answer is:
pathetic
'it's pitiful' is the definition.
(synonyms)
'father gets the twitch' is the wordplay.
'father' becomes 'pa' (pa can mean dad or father).
'gets' is a charade indicator (letters next to each other).
'twitch' becomes 'tic' (tic is a kind of twitch).
'pa'+'the'+'tic'='PATHETIC'
'when' is the link.
(Other definitions for pathetic that I've seen before include "Arousing pity or sadness" , "Feeble; inspiring pity" , "Sad - hopeless" , "Tip cheat - truly sad" , "Pitiable, inadequate" .)