Thinning the Herd

Why is it that loud, obnoxious people always travel in herds?  You round them up and make them leave the public areas of the library because they're too loud and disturbing other patrons and what do they do?  They walk outside and stand right in front of the entrance, smoke their cigarettes, and carry on their loud conversations without skipping a beat. That is... after they've called you every four-letter word known to man on their way out the door.