When I was growing up, our family - and the whole Milwaukee area, I think - used "soda" to refer to any soft drink. My cousins, who lived in a rural area, used "pop" for soft drinks.
My cousins were older, and were all jerks and bullies that used to beat us up when the families got together. And none of them were very smart, either. So to this day I think of someone who says "pop" as a dope.
It's totally unfair, but I'll probably never get over it.