bad taste in one's mouth

noun3

1. •
   A feeling that 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.
2. •
   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.
3. •
   A feeling of disappointment and frustration.