Why are people rude?!

Rude people annoy me so much! So I do a competitive sport and so in my sport we have PRIVATE lessons with our coaches. So I was at the complex where I do my sport and I was practicing before I had my lesson. And the SHE shows up. So this girl was named Kendal. So Kendal showed up and she is the most self conceited person that I've ever met. So supposedly she quit, but here she is at the same time my lesson is at. So when my lesson starts she right away comes over to my coach and starts asking him questions. Like, you see my standing here having a lesson and you think that you are so imortant that you can interupt. Like your not paying for this time, I am. So long story short I never said anything which I should have, but I don't like crying especially infront of my coach. And I knew I would if I said something so I satyed quiet until I was home and told my mom. She called my coach and told him and I think he said something to the her because she hasn't bothered me in my lesson since.