If I weren't familiar with carbonation...

…would a flat soft drink still taste nasty?

In my experience, yes. In beer vernacular, we call a flat beer (can or botttle) a “Skunk”. Gawd it tastes awful, even when cold.
'Course we drank them anyway, after all it was beer! :wink:

Y’all in North Car-o-lina are just plain wrong. Skunk is when you’re beer is skunky. I believe the fancy word is oxidized.

“Skunky” beer is typically the result of beer that has fermented too long or been overexposed to light. This is preferred by a lot of people and is the reason you see some beers in green or clear bottles (notice that green and clear-bottled beer both have a distinct aspect that brown-bottled beer universally lacks.)

I’ve never heard flat beer called “skunk”, “a skunk”, or “skunky”. I guess I’ve always just heard it called “flat beer” but, then again, who leaves opened beer lying around long enough for it to go flat?

For what it’s worth, real cask-fermented beer can be flat, if mishandled:

http://www.camra.org.uk/SHWebClass.ASP?WCI=ShowDoc&DocID=2243

Does it taste nasty? I don’t think it’s that bad, if there’s plenty of ice in the glass. Lukewarm soft drinks taste nasty (carbonated or otherwise), but so do most lukewarm beverages.

That’s very much a personal opinion. Plenty of people like lukewarm soft drinks just as much as cold ones (me included). The only reason I’ll have ice in a drink is if I’m actually hot.

IIRC: Carbonation reduces the apparent sweetness of a drink. There are plenty of soft drinks which are habitually drunked without carbonation, fruit juices and lemonade for example.

Skunk flavor is caused by ultraviolet light breaking down compounds in hop oils. Oxidation is a different but equally undesirable off-flavor. As the name implies it is caused by exposure to oxygen. The homebrewing literature I’ve read indicates that it leads to more of a wet cardboard taste.

There are plenty of ‘flat’ beers, although they are carefully brewed to taste good that way.

Soft drinks intended to be carbonated typically taste too sweet and bland when flat, because the carbonation is perceived on the tongue as acidity and it seems to help with the perception of aroma.

When I was a kid, I prefered A&W root beer flat, now it tastes way too syrupy sweet.

McDonalds Orange Drink = Flat Orange Soda

But with a different ratio of water to syrup, which is key. If you carbonate McD’s orange, you get a not good orange soda. Flat Crush et al tastes nasty.

I prefer all my pop flat and ice cold. If you were to look in my fridge you might see a two liter bottle of cola with the cap off at any given time.