Worst Sports Fans
Miami
Atlanta
Los Angeles
Miami and Atlanta teams routinely cannot sell out playoff games, plus Atlanta has the Tomohawk Chop. Los Angeles fans are notorious for coming late and leaving early and mainly being seen in between (and I don't want to hear the traffic excuse -- traffic in LA is no worse than that in Boston, New York, DC, or San Francisco).
I almost want to include Philly on that list -- they are knowledgable and passionate, but this whole tough Philly fan thing is vastly overrated. Being Grade A jackasses is different from being good fans. Remnember the Michael Irvin injury? It ended the guy's career. It was obviously a neck injury. They cheered his being hurt. They also take such pride in booing everything (ignorance as badge of honor) that they booed the Donovan McNabb selection.
My vote is for the aforementioned cities, in that order. Miami fans are almost comically bad. Atlanta fans don't even support winning teams. LA is an enormous market that is blase to the point of somnolence about sports.