What would you do if your roommate took his things at will?

When appropriate, you can try to "deal with a man as he deals with you". Of course, after you use the other person's things, you still have to say that you used them, which means that you actually know etiquette, and maybe he will have some clarity in his heart. When you tell him, you must grasp your attitude and tone. You should not take it too seriously. It can be said that you just used it casually or you took it by mistake and found it after using it, so you just told him. At this time, you can see his reaction directly. If he smiles and thinks it's nothing, just use it. He also volunteered that he actually used your things. If you can use them together, it's actually nothing. You can also say that you can buy it together and use it together in the future, regardless of whose things it is. If he is indifferent and angry that you used him, there is no need to continue to lose face. Just make it clear and use your own later.