Green’s Dictionary of Slang

(US) a driver prone to accidents, orig. using the fender to push other vehicles out of the way when parking in a narrow space.

1928		Miami Herald (FL) 30 Jan. 7/6: Don’t be selfish and crowd in and become a nuisance as a fender denter.
1957		W.R. Burnett Underdog 29: ‘Can you drive?’ [...] ‘The best,’ said Clinch. ‘All right. My wife is a fender-denter. You can drive her shopping’.