How can I not let myself get so worked up if I feel someone is a mild threat to my baby? Like a rude driver?

People in todays world are just rude and inconsiderate. Not all but a lot of people only care about themselves. Get this: my fiances good friend got married and i didnt really have a problem besides the fact she is way immature despite the fact she is 10 or 12 years older than the rest of us. Anyway they had their wedding reception and we showed up early (they had a private wedding - just the two of them) anyway we took my son's little ride on tractor ( he was just over a year at the time) anyway she was mad that nobody was going fast enough with the decorations and got in her truck and was driving way to fast. I had literally just picked my son up and she run over his tractor.... you best believe i didnt keep my mouth shut especially after the fact that all she had to say was i havent been used to a kid being here all day and you should keep a better eye on him.... o boy was i livid... and don't worry about all those crazy people.... every mother has the right to be protective of her children and if you feel the need to say something then do so!