It's wrong to use things without the owner's permission.
Tim's razor broke while he was getting ready to go to work.
Tim wants to finish shaving.
Tim asks Mark if he can uses his razor because his broke, and he needs to finish shaving.
Tim grabs his roommate Mark's razor without asking him and uses it to finish shaving.
Mark tells Tim that's fine, as long as he cleans it afterwards, he's happy to loan him his razor.
Mark notices that someone has used his razor and confronts Tim, and they get into an argument.