How do I approach a friend who is mad at me without knowing why they are mad?

Knowing that a friend is upset and not knowing why can be a very stressful or fearful situation, depending on what their normal reaction is. I can imagine that this makes communication more intimidating. However, there are definitely ways to approach communicating that will let your friend know that you care about how they're doing, are affected by their being upset, and want to learn more about the situation. Reaching out to them from a supportive perspective may encourage them to open up to you. If the friend is feeling hostile, they may need time to process the situation (even though you're not sure what it is) and return to being more calm before they're ready to communicate with you. Starting communication by pointing out that "hey, I noticed that you seemed upset, and your feelings are important to me, so I wanted to see if there was anything I could do or anything that I had done to contribute to it"; By letting them know that you're open to hearing their perspective, they, in turn, may feel more open to letting you know what caused them to feel mad. It's possible that there was a misunderstanding, and if this is the case, you might find out by opening up some peaceful communication

Sounds like you are wanting to approach a friend in a sensitive and non-threatening way. Just like each human has their nuances in how they communicate, think about how you best communicate and how your friend best communicates (e.g. do you write to communicate that you are upset, do you leave the room to communicate this, reduce your eye-contact). You may want to think about if there is something they are doing that is out of character and explore why you feel the negative emotion might be directed towards you. You could reflect on the times you've been angry at someone and did not say why - Did you think they did not deserve to know or that you felt what they did was so triggering? Its important to think about where you both really sit with each other as friends. I can appreciate this is difficult - do not ignore your instances and be willing to hear the other side. You are welcome to receive emotional support form one of our listeners