For rude people, just "Kill um with Kindness!" I also have been to stores where a couple of people will be standing smack in the middle of the isle with their carts. I just stand there patiently, and say excuse me, and pretty much say what someone else said here, that they make the isles to cluttered, which most of the time is true also. Why do they stack items in the middle of an isle?

But some people just didn't put their brains in when they left home, or they are just plain dumbfounded when they stand in the middle of the isle with their cart, and know you are trying to go by.
In my line of work I also have dealt with rude, snobbish people that don't return a "Friendly Good Morning, or Hello." There is one particular guard who when I enter in the morning I say "Good Morning!" Some days she acknowledges, and some mornings she looks sternly, and doesn't say a word. Just a bad "Hair Day" I figure. I am the type of person that speaks to, and trys to treat everyone with respect from the Janitor on up.
It takes only a couple of muscles to smile than to frown I've heard.