Definition
This idiom is used to describe a situation where someone's past misdeeds result in a negative reputation that is difficult to overcome, leading others to anticipate future bad behavior.
The media keeps highlighting his past mistakes; it’s like giving a dog a bad name, making it difficult for him to rebuild his image in the public eye.
Once you're labeled a liar, it's hard to shake that reputation; it's a classic case of giving a dog a bad name.
Because of his early criminal record, every job he applied for was rejected; it's a clear example of 'give a dog a bad name'.