The one that infuriates me the most:
"NV is an expansion to FO3"
No, it isn't. It has an entirely new world, quests, and characters. Never in my life have I even heard a rumour of an expansion that will give you as many or more playtime as the original game.
It makes my blood pressure rise a little myself. An Expansion is usually over in a couple of hours, and usually involves the same main character.
New Vegas is an entirely new characters story. People seem to forget that just because it has the same graphics, it doesn't always mean it's the same game.
I call them Shinyholics. The arch enemy of the Gritties, the people who rant and rave about too much shiny tech.