A person who takes an inappropriate amount of milk from the carton for his own satisfactory, leaving a very small ounce of milk inside the carton, not thinking of the others who live in the household.
By doing so, the next person who has a desire for cereal, pours the leftover milk into his cereal bowl, leaving an uneven bowl of milk and cereal.
It is basically the person, or cereal killer
, leaves a small amount of milk, and someone else attempts to eat cereal, but is instead left with little milk and a lot of cereal, blaming the suspect
Steve: Hey, you alright? Did you eat any breakfast?
Jake: No, man, it was because of that cereal killer
Steve: Don't worry, dude, you're not alone. You're not the only person who lives with a cereal killer. I live with one, too.