How to say that you have a stomachache gracefully?

Don't be too blunt, clearly show your situation. To express your stomachache gracefully, you can say "I feel sick", "I feel a little sick", or "I feel a little abdominal pain" and so on. These expressions are not too straightforward, so they are elegant. If abdominal pain is severe and symptoms such as vomiting and diarrhea appear, you should seek medical advice promptly. If you have a slight stomachache, you can try to rest and drink water.