"Goof" -- intentionally spreading false information for purposes of a joke. Saying that the city may change its name to Mountain Dew, California, or that it is recruiting a minor league baseball team to play in McKelvey Park are both examples of goofs.
"Fuck-up" -- spreading false information while thinking it's true. Maintaining that Mountain View has made approval of Home Depot's proposal to move into San Antonio Shopping Center contingent upon the company paying the city a quarter of a million dollars to establish a permanent day worker center, or that Home Depot has given the city a quarter-million unsolicited -- that is a fuck-up.
[UPDATE 7/13: This post has been edited in response to criticism in the comments section].