Hey there! I was lurking and saw your post. Full disclosures I do not have BPD but a relative does. I think I might know a few things that help. Personally I have anxiety that presents with anger and rage so I get it.
1. Assume positive intent when possible. Sounds easier than it is but if you practice it helps. Even finding silver linings even jokingly can help I.e. J at work is super bossy and annoying but at least I know she make sure the work gets done! That sort of thing. Be careful what you say out loud on this one lol.
2. Don’t feed in to vilifying or splitting. Most people aren’t all good or all bad. If you try to stay out of the always mentality and absolutes it will help. Also takes some practice to get it perfect.
3. Find a way to cope. I read. If I have a conflict I don’t know how to solve and am raging mad I research how others have dealt with my problem or I read and get perspective and realize it could be much worse. This works for me but find your thing. A way to self soothe. It sounds childish but it makes you feel stronger and empowered to fix your problem or at least brainstorm ideas. For the thing with your roommate you could have written down a plan of what you wanted to say the next day to let her know it made you feel violated. You’ll miss some opportunities on this one but that is okay use it when you are clear headed enough to apply it and with practice it will seem more natural when you are in crisis.
4. Research emotional intelligence or watch a video. I have taken a few of these types of classes online as e learnings and my God they helped me figure out how to deescalate even while raging.
5. Read the book Crucial Conversations. I just did a training on this book and it legit helped me figure out my emotions better and taught me how to confront an issue without getting to the point of raging. This book changed my life. If you adopt only one thing on this list it should be reading this book.
6. Be honest and open about how your disability/ disorder impacts you with the people who love you. Let them know how you trigger and how to help deescalate you.They want you to feel happy and loved. Help them help you. For instance I told my husband I need to feel heard by him so we now use to sandwich method in conflict. He repeats my problem back in his own words, acknowledges his role, and gives an apology then we end the talk by brainstorming what we both can do to avoid the issue in the future. This technique only works and continues if you also use the sandwich method when the other person has a conflict as well. So make sure you are putting in what your getting out of the situation. Think even Steven trade.
I hope something in this helps you. I am proud of you for looking for answers to your anger that is really awesome.