Literally translates to “eat candy”.
엿 is traditional Korean candy. In the late 1960’s Korean students had to take SAT tests to get into college. One of the questions asked what ingredients are in 엿. Many students got the answer wrong, and were unable to get perfect scores to enter into the university they wanted. So their mother’s made 엿 with the ingredients listed in the wrong answer and went to the ministry of education and told them to “엿 먹어!”. Thus is born a new way to say f*you in Korean.