Missouri. f#*k those idiots.
I think it is an issue of who you are around on a given day. My wife and I were at the Missouri game in 1997 when Matt Davison caught the kicked pass and NU went on to win. At that game the Mu fans were beyond nice to us --- it was a total pleasure hanging with the Tiger fans. they were great to us.
So, I'd guess a group of fans with too much alcohol or just that classic belligerent butt head can, as the minority, make the fan base look really bad. People are people. Generally though, the MU fans have always struck me as fine.