Much like its definition (spoiled milk), this term refers to a person who is past his/her expiration date. Not to be confused with mortality, instead, the term refers an undesirable individual. A person whose lack of social skills and poor general sense of hygiene impede contact for extended periods of time. People who fit the name are rude, smell bad (a foul odor permeates from the oral cavity) and have no sense whatsoever.
Don't stand too close to the nurse in the back, she reeks!
Yeah, it's her breath. She's rude too, she's a leche cortada.