Psychoanalysis

So here is the scenario- the car behind me slips to the lane next to me slowly speeding up with full intentions on passing me. This doesn't bother me because they obviously have some urgency, when I do not. There is too small of a gap between the car in front of them and me in the other lane so I lift my foot off the gas to make a little room. That's when they quickly accelerate and cut in front of me like their life depended on it and speed away. I don't mind being passed but it's that last little jolt that's irritating. Like they won over on me or somehow outsmarted me to push their way through the space like I wasn't willingly slowing down to let them over. 

I will probably never see them again AND it really doesn't matter. So why do I feel that small twinge of irritation?
It's nothing that ruins my day, but it does make me question....

What about the situation is frustrating?

Is there anything I could have done to avoid the irritation?

Why does it matter if my kindness is rejected? I should be kind no matter if it is received or not?

Am I just trying to control the situation? Like, am I "allowing" them in because I'm nice and I subconsciously think they should be grateful for my kindness?

What is the real problem rooted in?

I think it stems from a fear of being misunderstood, yes, a need to be understood. 

Why is that important? What other areas of my life does this affect?

Why am I thinking about this? Ha!

Why do I psychoanalize my actions, reactions and interactions?