foursquare now has a badge to reward users that like to hang in large crowds late at night.
Just Updated for November: Find Out How Many People Use 1,000 of Your Favorite Social Networks, Apps and Digital Services
Check-in to a venue with 50 or more other users checked in after midnight (it actually sounds a bit difficult) and you will get your shiny new foursquare Players Club swarm badge and receive the following message:
Stranger danger! It’s after midnight and this place is swarming. Make some new friends!
Enjoy and try to stay out of trouble earning this one!