I hate when people mumble. What is so hard about opening your mouth when you talk?

Why do some people feel the need to try and talk like this

Just open your freakin mouth and talk like this

I'm sick of it. Yeah, sure i have bad hearing, but its not all my fault that I have NO FREAKIN IDEA what you are trying to say to me!!!

I can usually piece together what people are saying by using what I heard and what movements their mouths are making. BUT WHEN YOU DON'T OPEN IT TO TALK I CAN'T!!!

Sometimes I just want to pry peoples mouths open to make them enunciate. I can't handle it. 

I try to be polite.

I say

"What was that?"

They speak without opening their mouth again

I say

"I'm sorry, I didn't catch that"

They mumble one last time

I say

"Excuse me, I don't understand"

They scream 

"I SAID..... ARE YOU DEAF OR SOMETHING?"

I say

"No, you just don't know how to open your mouth when you speak"

They say

"Well how was that?"

I say

"At least you opened your mouth"

But during that entire thing, I just want to get in their face, shove my thumbs in their mouth, pry it open and scream

"OPEN YOUR FREAKIN MOUTH WHEN YOU TALK!!! QUIT MUMBLING!!! GAHHHHHH!!!!

but i dont.