I reckon Nvidia fans come across as more obnoxious because they pay higher prices for "similar" performance cards. With the last gen it may be true, but I can see some people sticking to Nvidia and finding different arguements if AMDs hardware frame pacing works as promised.
With Intel it's a bit harder since they are better and their superiority is "justified" to an extent, but I still think the cost difference in the platforms is way higher than it should be. And Intel themselves are pretty obnoxious with the whole "new gen, new mobo" thing they have going.
And AMD - the fans often get into the price/performance arguement. Some need to understand that the concept of value changes with person and their income, but otherwise they're fine.
On the whole though most people are fairly reasonable, though they all have a slight bias/favour to one side or another.