Go off taking public transport? Tough! (6)
I believe the answer is:
robust
'tough' is the definition.
(thesaurus)
'go off taking public transport?' is the wordplay.
'go off' becomes 'rot' (I've seen this before).
'taking' is an insertion indicator.
'public transport?' becomes 'bus' (bus is a kind of public transport).
'rot' going around 'bus' is 'ROBUST'.
(Other definitions for robust that I've seen before include "Full and rich (wine)" , "Stout" , "Tough!" , "No-nonsense" , "'Hearty, healthy (6)'" .)