EUF scene from 1995 movie 'National Lampoon's Senior Trip'. A student riot breaks out during a high school assebly, and the lead singer of the band has her gown accidentally ripped off, exposing her bra and her unmatching -and huge!- panties. Extremely embarrassed reaction!
Starts at 9:12 of the video;
http://www.youtube.com/watch?v=JDveWvAqrVA