What music video is this?

I cant remember the name of the song but I remember parts of the video, It was about some high school reunion and a band was up on stage playing the guitar and drums while it shows flashbacks of them in high school showing them as outcasts and they got picked on, I remember one of them was a fat kid and in the flash back some girls put something in his drinking or food that made him poop himself. I hope you can help.