What is the meaning of idiomatic expression of bad taste in the mouth?

Think of having a bad taste in your mouth. The image is of something that is unpleasant. Something that "leaves a bad taste" would be something that makes you feel bad even after it is over. You hear this said often of someone doing something that goes against their conscience. "It left a bad taste in my mouth when I told that lie."
Think of having a bad taste in your mouth. The image is of something that is unpleasant. Something that "leaves a bad taste" would be something that makes you feel bad even after it is over. You hear this said often of someone doing something that goes against their conscience. "It left a bad taste in my mouth when I told that lie."