I can think of quite a few ones in regards to champagne (only because I'm closest to that wine)...
Rose Champagnes are sweet (This was the origin behind posting this topic)
Champagne in general is sweet (although it can be of course).
Champagne is really just a "social-gathering drink" but not a drink for food of any kind.
Champagne is "meant" to be frothy and consumed young (this is of course just personal preference but I will always take the nutty/caramel tones that aging imparts).
In fairness, there is also the misunderstood flip side - all aged champagne is good and is not as enjoyable if you drink it young.
Champagne is just a "white wine with bubbles" made from white grapes.
Champagne must be drunk out of a flute (I break this rule all the time using a Chardonnay glass)...
Dom Perignon is the be all end all of champagne (I actually DO love Dom Perignon and it's one of my favorite champagnes. But there is surely a wealth of other great champagnes that can take your breath away at a fraction of the cost).
Only big champagne houses can make great champagne (I'm guilty myself of tasting mostly house champagnes, but I do realize that the greatness of the wine isn't exclusive to the houses).
And probably some more I'm forgetting....
Jeff