It's wrong to use things that aren't yours.
Sam is very tired and hungry upon arriving home after a long day of work.
Sam wants to avoid using too much energy making dinner.
Sam orders a pizza as an easy fix.
Sam uses his roommate's leftovers with a couple other ingredients to make a quick and easy meal.
Sam's roommate enjoys the rest of his leftovers.
Sam's roommate is disappointed because he was looking forward to eating the leftovers.