As reported on their website Improv Everywhere staged an event and… :
Today’s No Pants was halted by the cops about halfway through. One frustrated cop freaked out and called in 25 more. 8 were ticketed and summonsed to court, 6 of the 8 were handcuffed and traveled in a police van to a precinct. Everyone has been released and is fine. More info as it develops. Keep checking this page, and the comments below for updates from everyone involved.
There’s a wonderful Flickr photo set available.
I’m still wondering what they were actually arrested for.