When someone doesn't agree with your opinion anymore and just shuts you down and, basically, tells you to go fuck yourself for being an individual. It usually makes you spend the weekend feeling bad about yourself.
Casey didn't want to hear anymore about my thoughts on his favorite football team so he said "On a serious note, I'm out having fun and having a good time, you're really not being cool and pissing me off just leave me alone while they play." and, upon trying to express your opinion of a tv show says "oh, shut UP, I can't deal with this" and then you feel bad inside for having tried to be a part of his life. It was all extraordinarily dismissive.