The only sunglasses that really bother me when someone wears them for long conversations are the mirrored ones. I find it distracting to see my reflection and have them shining at me constantly- and they completely block the eyes as well. Anything else besides the reeeeeeeeeeeally dark ones wouldn't bother me in the least. In a gas station (I was a clerk for a few summers) it wouldn't even have registered with me that you had them on.
I agree with you that I like to be able to see someone's eyes if we are going to have an extended conversation (so I would prefer someone remove dark or reflective sunglasses if we're going to talk a while).
This reminds me of my sixth grade teacher (back shortly after the invention of the wheel). He was an older man who always
wore very dark sunglasses all
the time - inside and outside. It was a bit unnerving because one couldn't tell if he was looking at you or not when he was talking with you. The few times I remember anyone asking about them, he would joke that their purpose was to allow him to observe students without them realizing he was watching. Looking back now, as an adult, I suspect that he may have had a medical problem with his eyes.