a feeling that something is false or unfair, a feeling of ill will

Got the covid-19 vaccine

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.

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..

an ex that u wish u never dated

The feeling you get after working as a fluffer!