Being able to express your grievances to someone is one of the most useful skills to know. Most times, we will say things like, "You make me so mad." In essence, no one makes you feel anything. You are responding emotionally to what someone has said and/or done. This is valid. The way to confront this matter would be to say, "When you said/did ___, I felt ___." We want to identify how we feel via a cause-and-effect statement and not a statement that throws an accusation at the other person, creating the space for the other person to get defensive.
A very useful skill to have socially is to know the difference between acceptance and approval, and how to utilize this when faced with negative events. Very simply, acceptance is acknowledging that something just is, with no personal attachment (i.e., you are wearing jeans). Approval is the positive personal judgment of something (i.e., your jeans are so stylish). When we are able to approve of something, acceptance comes with it. If we don't approve of something, we can learn to accept it. However, if we don't approve and we don't accept, this is when our social skills diminish exponentially.
Apologizing seems to be one of those things people either hate to do or fail at miserably. I love it when folks apologize and then try to rationalize their behavior by blaming you or someone else. "I am sorry I hurt you, but you ..." This is not an effective form of apologizing. Proper apologizing is doing just that: apologizing. It does not include any rationalization. In other words, just apologize. The proper way to apologize would be something like, "I am sorry you feel this way." If you want to lend support, add something like, "Anything I can do to help?" Leave it at that. Once the wounded person is able to process, then maybe you can bring up, in a non-threatening way, how you can each change so that future hurts can be possibly avoided.
Rejection is one of the things I have worked on the most in my life and is a chronic issue for clients in my practice. The best suggestion I have learned about rejection is to recognize that the person/agency is not rejecting you as a person. They are rejecting the notion of you and them in some sort of union. Being able to reframe rejection from a subjective experience to an objective one alleviates so much pain.
In dating and relationships, rejection seems to strike us the hardest. Once again, we are called to be more objective about the matter. Flip the mirror to you. Have you been attracted to everyone who was attracted to you? The answer most likely is not. Does it have to do with the other person solely? Usually it involves a variety of factors, the main one being your own personal tastes and where you are presently in your life. If we are not attracted to everyone who is attracted to us, how can we expect that folks are automatically going to be attracted to us just because we are attracted to them?