The first down chant is something a lot of the dome takes part in. The Sioux Suck part, if I had to guess, is maybe 25% of the student section.
When I got to school in 2010, that was not even a thing. Maybe 2011 or 12 it started to take off.
I don't see any problem with it. I have been to parties/bars/party buses in GF where a *&%$ the Bison/Gophers chant starts up. Again, good natured...really no different from random "USA, USA" chants breaking out.