Best friend in back of car, passenger getting lip busted (8,7)
I believe the answer is:
springer spaniel
'best friend' is the definition.
(dogs are 'man's best friends')
'in back of car passenger getting lip busted' is the wordplay.
'back of' says to take the final letters.
'getting' means one lot of letters go next to another.
'busted' indicates an anagram.
The final letter of 'car' is 'r'.
'in'+'r'+'passenger'+'lip'='inrpassengerlip'
'inrpassengerlip' with letters rearranged gives 'SPRINGER SPANIEL'.
(Other definitions for springer spaniel that I've seen before include "might this be barking?" , "one used to raise game" , "breed of dog" .)