The unemployed 53-year-old woman - a saleswoman by trade - told staffers at a Cologne car dealership she wanted to test the €92,000 luxury vehicle - then never brought it back.
The car was found five days later with an empty petrol tank.
The municipal judge cited the woman's narcissistic personality disorder on Friday to justify the relatively mild sentence.
Her lawyer had argued the dealership was partly at fault for letting his client take the car without running a credit check or demanding a security deposit. All she had to do was show her driver's license and photo identification.