Mock extremely disreputable journey (6)
I believe the answer is:
deride
'mock' is the definition.
(deriding is a kind of mocking)
'extremely disreputable journey' is the wordplay.
'extremely' suggests removing the centre (only the extremes of the word are used).
'journey' becomes 'ride' (ride is a kind of journey).
'disreputable' with its centre taken out is 'de'.
'de'+'ride'='DERIDE'
(Other definitions for deride that I've seen before include "Ridicule, scoff at" , "Speak of with contempt" , "Laugh at or make fun of" , "'Mock, sneer at (6)'" , "Knock" .)