Saying one type of fan is any worse than the other is ludicrous... but it certainly runs in cycles. For a long time, Sega fans were the worst because they were, by necessity, the most defensive. SegaCD, 32X, 2 failed consoles, everyone making fun of them for their purchase (not even just the hardcore)...
The pattern here is that whatever you purchase, if your purchase is failing in terms of mindshare, you're going to be ridiculed for it mercilessly. First it was Sega fans, followed by Nintendo fans. I got very bored trying to defend my purchase of a "LameCube", but I did get very despondent about how you couldn't say a single positive word about Nintendo without being looked at like you're retarded.
And THAT, folks, is where fanboyism takes its strongest root. If you spend more time being laughed at for what you enjoy, OF COURSE you're going to feel a need to strike back.
Nintendo seems to be on an upturn now, which never happened for the Sega fans, so you can imagine that after 10 years of ridicule, Nintendo fans are seeing an opportunity for a shred of vindication. Do they take it to obnoxious levels sometimes? You bet. But if you ever made fun of someone for owning a GameCube or a DS before its market upturn, you only have yourself to blame.
Conversely, we're starting to see this level of defensive behaviour in Sony fans, as they are now the ones being mercilessly persecuted. And lo and behold, we're seeing similar behavior from Sony fans that we did from Nintendo fans during the GameCube/N64 era. Surprise surprise.
Doesn't take much to put two and two together, folks. If you want it to stop, here's what you gotta do: