hey you. yeah, you
now that I've got your attention: I'd like to say that I think you're pretty great. thank you for being a cool person and living your life. You deserve all the happiness that will come to you sooner or later and more.
Or hear me out – express that you're in a bad mood, don't want to talk, and you need some time alone. Any of those options work.
Getting ignored without knowing the reason why hurts a person more than you would think.
Treat others how you want to be treated.