If i combine the individual word meaning, it doesn't feel make sense. Someone said this is a derogatory term but not commonly used these days.
(1)되먹다 : 다시 먹다 eat again
되먹임 (noun) input again
내가 남긴 물을 엄마가 되먹었다. Mother drinks again water which I did not drink completely
(2) 막되다 be rude.
그애는 그렇게 막된 아이는 아니다. He is not rude as much as we think.
(3) 돼먹다 bear nobleness (cf 돼먹지 않다 It is out of standard rules)
그 애는 돼먹지 못한 아이다. He is a child of bad demeanors.