Here's my vote for the worst set of moves in the Sicilian line that were ever played on the record. This is in the lichess database. Here's the opening sequence:
Be careful plugging that into your chess engine, it might just retire and walk away.
Accomplishments include players reversing the evaluation every turn (after the initial turn of Sicilian opening); a gracious queen blunder; and ignoring mate-in-one not once, but twice with the same move!
That being said, no single game ever made each of those mistakes, they were all just (real!) individual, blundering responses to each position. **The only game to reach this position**, did not, in fact, get there that way:
But it was still swinging around pretty wildly for a pair of 1200+ players!
Some analysis of the pasted-together line is probably useful here, if you want to learn from these mistakes:
2. ... g6
The impulse to fianchetto the king's bishop out through g7 is a good one, but the weakness of the f7 pawn to attack is too severe. You are better off focusing on pawn (e6, a6) or knight (Nc6, Nf6) development instead.
3. Qf3
Okay, if you think that your opponent just doesn't see the weakness, this isn't a terrible bait. Yes, it's a weak move, but the potential upside is large. Still, maintaining principles would still be best. You have pawn (c3, d4) and knight (Nf3, Nc3) developments that you could make instead.
3. ... Bg7
This is mate in one because of `4. Qxf7#`. If you absolutely must do this, at least block the bishop and give your king an escape-hatch first with, `3. ... e6 4. d3 Bg7`.
4. d3
This is obviously bad because you didn't just win the game in one, but it's also bad because it's just a terrible move. `Bxf7+`, `d4`, and developing either of your knights to ANY available position would have all been far better moves, even if they missed the win.
`d3` is terrible, though, because it closes in your position without any real advantage, while also reducing your tempo to develop your back-line, unless you're looking to long-castle, which isn't really advisable, here.
4. ... Nc6
The only problem here is that you haven't resolved the problem from before, and white can still win in one move. You need to address the combination of your king's lack of options and the f7 pawn's vulnerability.
5. c3
Again, white blocks in more of their space without developing any new control over the center. Ignoring the fact that they didn't just win the game, it's still a bad move, and all the advice from before still applies.
5. ... d6
On the positive side, you solved your mate problem by giving the king an escape-hatch. Bravo! But you didn't block the bishop's line of sight to f7, so when `Qf7 Kd7`, the queen is just going to take the bishop, and unless you move your knight out of the way so your queen can protect the rook, they'll take that too!
5. ... e6
This is even worse than d6 was! The queen is blundered immediately, and with great efficiency! Remember, when you move a piece that was under attack, always ask, "what does that attack now see?" #games source