Well, as i see it, part of the problem is that your goal is to not offend. Its understandable, but only to a certain extent. Reality is sometimes you have to offend people. There's no way around it unless you just keep your mouth shut at all times. And all that does is turn you into a frustrated person and likely a doormat.
And if you're confronting them about something they have done wrong, then no surprise they aren't receptive. Most people are not receptive to that.
These people offended you in some manner, yet they didn't give a second thought to how you feel, yet when the tables are turned you become concerned about offending them. These people showed no concern for you when dealing with you, so you also should not place a lot of emphasis on not offending them. If you can find a way to deal with it without being offensive, great, but if not then you just need to speak up, step on toes and not worry. And i'm not talking about eye for an eye, but just that you have a right to speak up and share your concerns or problems. Speak up, be bold, and if they don't like it then they need to rethink the way they treat people to begin with.