When you live in such a small town that you run into someone you know EVERY time you go out. Short for "you can't swing a dead cat by the tail without hitting 2 people you know." Basically means you live in too small a town. In gestured form is done by a circling of one hand in the air like a lassoing action.
I went out to eat with my friends and the waitress comes over and says, "hay, I went to high school with you." My friend says, "you can't swing a dead cat."