It was at LES sometime in early 2000's, IIRC. They went from bathroom to bathroom trashing the place until finally security caught up to them.
Of course, this pales in comparison to Utah fan behavior. The worst fans I've ever encountered were Utah fans in the following games:
1. BYU @ USU, 2010
2. BYU @ Utah, 2010
3. Utah @ BYU, 2007
4. BYU @ Notre Dame, 2012