I get this all the time, too.
Car drivers change lanes and are looking for other cars to be in the way, not motorcycles. No one knows its your birthday, and no one is trying to kill you. If fact, had she hit you, she would be sitting beside her car, crying. Upset that she hurt someone.
I had a very professional lady do the same to me. I could see her id hanging around her neck and recognized it as a dr's id from the local hospital.
After cutting me off, I was beside her at the stop light. Her window went down and she shouted, "I'm sorry! "
I said, "No problem..at least you could have repaired me!" She laughed, and we moved along. You drive on to the next block to repeat the process.
When im on a road like that, I'll go as fast as necessary until I am alone. Not bunched up, then cool it in my own, open spot.
You did a good job in being aware and ready, but speed up, or slow down to avoid that situation.