an unmade bed is a bed which has been left in extreme disarry but is often used as a derogatory term to describe someone who looks as though they were traipsed upon by a herd of elephants after getting dressed because they're lazy and unconcerned about their appearance. Usually this person must be larger in size for it to properly apply but there can be exceptions.
Hey, did you see Melissa this morning? She looks like an unmade bed.
Doesn't he own an iron? He looks like an unmade bed today.