An idiom used to express feelings of regret and remorse, stemming from a realisation that one has willingly participated in behaviour that has led to an unforeseen and morally reprehensible outcome. The idiomatic use of eating serves to convey both the initial positive, tasteful, experience, as well as the negative, distasteful, after-effects.
Clearing the rain forest is how I make my money, but seeing locals driven from their homes has left a bad taste in my mouth.
Having an unpleasant taste in youre mouth, mostly ment as a methaphore, but sometimes literally. It can be caused either by a feeling or an actual event.
Either way, if something gives you a bad taste in the mouth it is always bad.... really bad..
Catherine said: A beating from the love truncheon left a bad taste in my mouth