Look like death warmed over

Origin

Imagine a meal, already cold and unappetizing, that's been reheated only to become even more dreadful and unpalatable. That's the rather ghastly imagery this phrase conjures for someone appearing utterly dreadful. While its exact moment of coinage is a bit hazy, likely emerging in the early 20th century, the idiom powerfully plays on the inherent unpleasantness of "death" itself. The addition of "warmed over" intensifies the horror: it implies a state even worse than being merely dead, a ghastly reanimation or a prolonged, pitiful suffering that leaves one looking profoundly unwell, as if they've come back from the brink only to linger in a more wretched condition.