My clothes. When I was living at inicial at the time, my sister, who is 7 years younger than me, and I had to share a bedroom and she kept stealing my clothes from me, it always made me so mad mostly cause she never asked. I couldn't steal her clothes, since she was and still is smaller than me but somehow she could wear my clothes.
Most of my stuff. I used to let people borrow things, but got burned quite a bit. So now, I prefer not to lend any body something - if it is something I can live without, I will give it to them. Same thing if someone offers to lend me something, I say no.