ANSWER:
It is insane to believe that such an act can be kufr!
How does Satan do this? How does he manage to make Muslims so ignorant to the extent to think that if one feels embarrassed to eat rice with his hands in front of people makes them kafir?
Kufr is to exit the fold of Islam by rejecting some of the pillars of Islam or insulting Allah, Quran or the Prophet salla Allahu alaihi sa sallam or by associating others with Allah in worship etc.