Facebook has always been creepy. But now its allowing you to be creepy, too! The site started rolling out an optional new mobile feature Thursday called Nearby Friends, which alerts you when your friends are nearby (and vice versa.) But if you fear weirdos, dont worry: The feature will only load if you opt-in and turn it on. Facebook also lets you decide which of your friends can view your location, and those friends can only do so if they allow you to view them too.