he should've screamed, then told her he couldn't hear how loud he was

Substitutes can be a but dense and, no pun intended, but selectively deaf. I once had one send me to my assistant principal because she insisted that I was covering for boyfriend (which I didn't have) by answering to his name during roll call because I have a name that at the time was more commonly a boys name. It didn't help that my classmates in that period were assholes who egged her on.

this is tumblr bruh, like half of it is bullshit. but it's funny :P

I think he's just saying he can't understand her

Ah gotcha :)