Alright, we have an election-related riot, so it does happen:

http://www.rawstory.com/rs/2012/11/07/ole-miss-students-protest-obamas-re-election/

A protest at the University of Mississippi against the re-election of <the President> grew into crowd of about 400 people with shouted racial slurs as rumors of a riot spread on social media. Two people were arrested on minor charges.

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Police were initially alerted to Tuesday's uproar by people who saw Twitter posts about it. The students were told to leave, but about 100 came back later. One person was charged with public intoxication and another with failure to comply with police orders. There were no reports of injuries or property damage.