It's wrong to use your roommate's things without their permission.
Jeff has been stuck inside all day, and he thinks he should get some fresh air.
Jeff wants to go for a bike ride.
Jeff's bike has a flat, so he decides to wait until his roommate Ben comes home to ask if he can borrow his bike to go ride.
When Jeff sees that his bike has a flat he decides to take the other bike that belongs to his roommate Ben.
When Jeff asks Ben if he can borrow his bike he says yes and tells him to have fun.
When Ben gets home and sees that his bike is missing he thinks that someone stole it.