Bought a three pack of bone folders last year just for this. Keep one in the kitchen junk drawer. Kid uses it for bookbinding, I use it for creasing paper patterns. Stuff like that is meant to be shared in a house. Annoying, but cheaper tools solve it.
That three pack strategy is smart. I do the same thing with craft knives, always buying a five pack because the good one always walks off. It's just part of the deal when you have more than one person making things in a house.