Overshare has nothing to do with your location and things you are doing at that location and  that is a good thing I guess… The Overshare badge is possible to earn on your first day of using Foursquare and can be earned along with the Newbie, Adventurer, and Crunked badges.

Overshare badge foursquare

To earn the Overshare badge, all you have to do, is actually earn your Adventurer badge very quickly, so get in a car, on a train, on a bike and get going. The Overshare badge is given when you check into more than 10 locations in less than 12 hours. So as you can see if you start using Foursquare, on day one and start checking in at night and visiting many places you can unlock 4 badges in one day including the overshare badge, and that is exactly what happened to me.