Return the favor, since by that logic it's also within your right to break his stuff because you also live there. Alternatively, see if you can buy and install a lock with a key on your bedroom door and lock it every morning when you leave. Not a lot of details about what your living situation is, but if you live with your parents and this is an issue of favoritism, the lock is probably your only option, short of just beating your brother to death with a baseball bat while he sleeps. Since, for some idiotic reason, allowing one sibling to abuse the other isn't considered child abuse on the parents part. If you don't live with your parents and are living with your brother to save on costs, I'd suggest cutting your losses and see about moving with a friend short term until you can find somewhere else. That said, if you have any close friends with rational, decent, caring parents, explain the situation to them (if this is a repeating issue) and see if they will let you stay over frequently and/or keep important items at their house.