A lady purchases a dog  

My sister-in-law, a truck driver, had decided to get a dog for
protection. As she inspected a likely candidate, the trainer
told her, "He doesn't like men."

"Perfect," my sister-in-law thought and took the dog.

Then one day she was approached by two men in a parking lot,
and she watched to see how her canine bodyguard would react.
Soon it became clear the trainer wasn't kidding. As the men
got closer, the dog ran under the nearest car.