As I let the words roll of my tongue, "acting offended" sounds just awful doesn't it? Only a Machiavelli would admit to acting offended to achieve their aims! "Getting offended" needs to be seen to be from the heart - as if you really had been torn kicking and screaming from the womb of rational detachment. Effecting this obviously requires extremely good acting.
Being offended is a good tool. It is much better tool when used logically and by choice. Don't think of it as acting in a performer sense, think of it as acting in a sense of taking actions.
There doesn't need to be any disingenuity there, it can be an honest response even though it is a logical choice to display that response.