They say, keep your enemies close. We say, sure—but not, you know, too close.

Because there are certain people who, if you're given the choice, you'd just as soon not bump into. Your ex. Your archenemy. Inigo Montoya.

If only someone had invented a way to know where they are at all times...

Introducing Avoidr, a clever new Foursquare app that helps you keep tabs on your archenemies, available now.

You'll start where Nixon did: by making an enemies list. (Or, in the app's terms, people who are "dead to you.") Then, you'll search for them on Foursquare through the app itself—and as you go, you can assign them ranks, from "jerk" to the dreaded "cancer." (There is no "six-fingered man who killed my father." Not yet.)

Once your enemies are properly classified, you'll be ready for the next and most important step: when you're ready to go out, click on the app and it'll scan Foursquare to give you a list of places marked with the distinct stench of evil, the kind you've long associated with your bitterest enemies.

And, okay, a few of your friends.