That's grounds for a car-keying. Or at the very least, kicking him out.

Once I asked my mother why we had to clean our plates and mugs, when they would get dirty again the next day. But that was when I was six years old.

Make his drinks with toilet water, if he can't see any dirt, then it must be clean

Actually technically it does mean it's clean. Clean is defined as free from all visible debris. However it is indeed not sanitized. And that's actually far more important.

Time to get a new roommate.

Buy him paper plates, cups, and bowls, and plastic utensils. Refund yourself by tacking the expense onto his half of the rent.

Put a child proof lock on your cabinet since you're obviously living with a child.

Kick him out or buy paper plates.

Put locks on your things or kick him out

Then make him buy his own plates!