Sandals and socks don't mix

So I saw someone today where sandals with socks. Explain to me why people do that and why it bothers me so much. You wear sandals when you're not supposed to where socks. If you want to wear socks, get some slip on shoes then. I will say though, sandals and socks are okay if maybe you're going out to get the paper or a trip to the car, but not when you're out shopping.