It's bad to use someone's property without permission.
Caleb was at his friend's house for a sleep over when he realized that he forgot his toothbrush.
Caleb wants to brush his teeth.
Caleb calls his mother and asks her to bring his toothbrush to his friend's house.
Caleb goes to the bathroom and uses his friend's toothbrush to brush his teeth.
Caleb gets his toothbrush from his mother a half hour later and is able to brush his teeth.
Caleb catches strep throat from his friend and has to go to the doctor.