Based on this comment I'd like to know which openings, if any, are considered unplayable (i.e. lost) for black? My own understanding is that in some opening lines it's harder for black to equalise, but are there any that are completely lost, assuming that white plays perfectly?
Your question is somewhat hard to answer, because it depends on what you consider "an opening" to be.
Obviously, there are openings where black loses -- consider the typical Scholar's Mate, 1.e4 e5 2.Bc4 Nc6 3.Qh5 Nf6 4.Qxf7#.
But, you will probably think, nobody with any knowledge of the game will play like that! And that's reasonable. But it is an opening, isn't it?
And if you mean "are there any commonly played, theoretical openings where Black loses?" then there are very few indeed -- after all, why would black play such an opening? Once some line is refuted, almost everybody stops playing it.
Ultimately, a lot of openings in chess will result in black losing, if both players play perfectly. It might not be your fault, just that black starts off one tempo behind.
I don't agree with that at all. Chess is considered by most people to be a draw at best play, and commonly played openings aren't losing. They may be slightly worse, but that's not the same as losing, not even with perfect play -- it just means that black will have to defend most of the game without much chance of winning himself.
The fool's mate, if white recognizes it, will put black at a severe disadvantage, of the checkmate kind.
[White "Mater"] [Black "Fool"] [FEN "..."] 1. e4 f6 2. Nc3 g5 3. Qh5#
Any variation of this where the black King's diagonal is wide open will suffice. The same can also happen to white, but you asked about Openings for black, if you consider this an opening.
There are no common openings that are considered lost for Black with best play. Katerina's comment was an exaggeration (at least according to the opinions of modern chess players). The most common opening that I can think of that is considered basically losing is Damiano's Defense (1.e4 e5 2.Nf3 f6), and pretty much no one plays that except as a joke.
One bad opening that usually causes Black to lose is 1. e4 e5 2. Nf3 f6.
White can play 3. NxP!, and if Black captures the N, he succumbs to 4. Qh5 ch Pg6 5. Qxe5 ch forking king and rook.
More often, Black ends up losing his e pawn, and while he can get it back, his development will be crippled while he is doing so.
Looking at Fritz upon White's first move, the first move gives White a slight advantage...but not an advantage that leaves Black in a position where Black would lose unless White makes a mistake - if both play perfectly, it will be a draw. If an opening is so bad that it leaves Black at a loss unless White blunders, it wouldn't be an opening that anyone would play, especially these days with such fine tunes computerized analysis of opening and opening theory. I play: Alekhine against e4, Benko Gambit against d4, and as white...right now, Dunst or Larsen or Kings Indian Attack....don't know my lines for all the potential e4 possibilities yet.
If you define an opening as "any moves that you can play during the first 10 moves" then there are plenty of openings where both white and black can get a lost position after 10 moves. Assuming that white plays perfectly, then black will be in trouble in many "openings".
Chess has been around for a while and the opening theory has taken big steps forward. Today, the openings are divided into systems and variations, some of them as deep as the first 20 moves. With white playing perfectly, black should play accurately or will otherwise fail to equalize. Yet, playing fairly accurately, I cannot think of many established opening variations that lead to objectively lost positions for black after e.g. 10 moves.
In a practical game between two human players, as long as there is room for play and counterplay, all three results are possible.