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neigh•say•er noun \ˈnā-ˌsā-ər, -ˌser\

A Denver Bronso's fan who habitually expresses negative or pessimistic views of an opposing team.

To neighsay

See: nay•say•er
Broncos Fan: Those Seacocks don’t stand a chance against our Broncos with Peyton Manning and the #1 offense! This Superbowl is in the saddlebag!

12th Man: Quit being such a neighsayer. You know our #1 Defense and the Legion of Boom are gonna kick Denver's ass all up and down the field.
by @Thanatos February 03, 2014