You shouldn't use other peoples stuff without permission.
Stacy, whose car has broken down just before going to work, is roommates with Jill, who has a bike.
Stacy wants to borrow Jill's bike.
Stacy asks Jill if it is OK to take Jill's bike to work today.
Stacy takes Jill's bike without asking and rides it to work.
Jill allows Stacy to borrow the bike, and Stacy can get to work and back.
Jill calls the police and reports the bike stolen, and kicks Stacy out when she discovers Stacy took it.