When someone's shameless behavior offends you, ask yourself this question right away: 'Is it possible for the world to have no shameless people?' Of course not. So don't wish for the impossible. This person, whoever they are, is one of those shameless ones that must exist in the world. The same goes for sneaky people, dishonest people, and everyone else who offends you. Keep reminding yourself of this. When you accept that these types of people must exist in the world, you'll find it easier to be gentle with each individual. Here's another useful practice: whenever this happens, think about what virtue nature gave us to handle this particular vice. For example, nature gave us kindness and gentleness as medicine against ungrateful people. And for every other type of bad behavior, nature gave us some other special ability to deal with it.
When at any time thou art offended with any one's impudency, put presently this question to thyself: 'What? Is it then possible, that there should not be any impudent men in the world! Certainly it is not possible.' Desire not then that which is impossible. For this one, (thou must think) whosoever he be, is one of those impudent ones, that the world cannot be without. So of the subtile and crafty, so of the perfidious, so of every one that offendeth, must thou ever be ready to reason with thyself. For whilst in general thou dost thus reason with thyself, that the kind of them must needs be in the world, thou wilt be the better able to use meekness towards every particular. This also thou shalt find of very good use, upon every such occasion, presently to consider with thyself, what proper virtue nature hath furnished man with, against such a vice, or to encounter with a disposition vicious in this kind. As for example, against the unthankful, it hath given goodness and meekness, as an antidote, and so against another vicious in another kind some other peculiar faculty.