Why does this never happen to me??? The only people who ever talk to me in the checkout line at the grocery store are old people telling me how cute my kid is. Am I shopping at the wrong store? 
Yeah, I wonder about that too.
I usually have two sorts of experiences in check-out lines.
One is that when people already know who I am, they ignore me as if I'm not there, as if I'm part of the natural environment or something.
This isn't rudeness; it's that if they know who I am, they know I can't hear, and wish to spare me draining myself physically and intellectually responding to courtesies.
The other is when people have no idea who I am, but then my voice, when speaking to the cashier, rouses their interest. They stare and stare and stare.
And then after I've left, the cashier explains, "He's deaf, you know."
After which they stare and stare at the door out of which I've just walked.
A few comment something along the line, "Well, he speaks the most precise, the most clear, of anybody I've ever heard....."
I don't overhear checkout-line conversations; apparently at times I cause them.
