This is what works for me, your experience may vary...
1. I'm vigilant to be riding in the best possible situation, be courteous to the other drivers, ensuring that I am following the law and best practices of cycling. That way, I KNOW I'm (probably) not doing something wrong or dumb.

2. If a situation does happen, I try to remember that their reaction is not personal to me, it's personal to THEM. You're just some person on a bike, "inconveniencing them, their time, their drive"
If you're following step 1, it has nothing to do with you. It has everything to do with them, because all their thoughts are about them. Typically someone who lashes out like that is in a selfish mindset.
So, if I'm doing well with #1, then I'll usually feel pity for those that lash out without a proper reason, for they do not have a more enlightened mindset to think of others.

As for dwelling on it:
I sometimes have this problem as well. The most effective actions for me is to go into my "calming routine." I think about and check my muscles one at a time to see if they are tense, if so, I relax them... Shoulders, neck, arms, hands, face, back, hip-flexers, etc. "I'm a leaf on the wind..."
Then I'll pay attention to my breathing, to ensure it is slow, smooth, and rhythmic; and at the tempo that is best for what I'm doing. Try to slow your breathing, it will help to slow your heart rate.
Then I think about my cadence and how my cadence and breathing are syncopated

After that I'll move my thoughts onto the rest of the route, ride, or whatever I wish.