I know someone who would use her husband's placard so she could park in a handicapped spot. She wasn't handicapped in any way, and he wasn't in the car.
This was pure abuse. He's now deceased, so that scam has ended.
We went to dinner with neighbors. She has a handicapped placard. We drove and DH was going to drop the neighbors off at the restaurant's door and then go park. She whips out her placard and wants him to use it. We said no - we'd drop them off and let someone who really needs the space have it. I always did this when I was with my mother. She had a placard, but we never used it if I was driving. I dropped her off at the door.