You know the type, talks loud sometimes, needs things repeated. That's me, and Jerry Seinfeld too.
Why do I always have to say “excuse me” when I can't hear what someone is saying? Why? Am I guilty? Did I inconvenience you? “Excuse me? Pardon me? I'm sorry?” Why can't I just say, “Nope. Not loud enough.”
So, as a fan, I gave it a try, just a blunt, “Nope, not loud enough.” It's surprisingly usable in a public-facing service role.
Here's another one. “Hey, use your outside voice.”
In regular conversation, the first one doesn't come across as rude as you might think. The second is bound to draw an eye roll, but it gets the job done. The catch is, they may start talking to you in a loud, slow, mocking tone from that point on. Apparently, if you can't hear them, the next step is to find out if you can understand them.
Edit;
Having pilfered the joke, I wanted to try out my alternative punch line and report on my IRL experience. U thought it necessary to cite the source, since that's where I got the idea. I wasn't aware it was in the public domain, and wound up in this strange position.