Inconsiderate driver (7)
'inconsiderate driver' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for road hog that I've seen before include "Selfishly aggressive driver" , "Boorishly reckless driver" , "Driver who obstructs others" , "Driving pig?" , "Mr Toad, for one" .)
(Another definition for roadhog that I've seen is " Reckless driver".)