Particularly those you live with.
DH will never use a clean knife when he uses the butter or cut off what he needs first. I loathe crumbs in butter. He is the same with marmalade. The only way to deal with him is two butter dishes and two marmalade pots which he is forbidden to use.
If only I can find a Work-around for 40 years of leaving every cupboard and door open in every room.