bad taste in one's mouth

Etymology
Refers to the feeling of nausea or its aftereffects.

Noun

 * 1)  A feeling something is morally despicable as to cause nausea.
 * The more I thought of my orders, the more it left a bad taste in my mouth.
 * 1)  A feeling of guilt, responsibility, or embarrassment as to cause nausea.
 * Knowing that I had inadvertently aided a killer, left me with a bad taste in my mouth.
 * 1)  A feeling of disappointment and frustration.