My roommate and I are sharing a room, but I didn't sign up to share a damn towel😭. Every time I find my towel damp, I can guess what happened. How do I politely ask them to stop using my stuff without starting a whole argument? I need a tactful way to handle this.

My roommate and I are sharing a room, but I didn't sign up to share a damn towel😭. Every time I find my towel damp, I can guess what happened. How do I politely ask them to stop using my stuff without starting a whole argument? I need a tactful way to handle this.