ouch!
Post your most painful losses!

My most painful loss is either where I was up a queen and a rook and blew it or when I was down so many a rook, bishop, and a few pans and I missed a mate in 1. Both were OTB so I can't post it. Both in the last month.

how on earth did you get so many rating points in 1 day? Anyway here's my most painful loss:
I really blew it.
Why did black not take the rook on move 57?
not a loss but i had draw because i accidentally clicked yes when the guy was spamming it every move in clearly lost spot ( i had rook and he just had king)

I mean, it's not particularly instructive, and the game is years old, but there's this one. Honestly, it still stings a little today.

The moment when I abruptly realised that the Meissner effect for the superconductors existed (so much for attempting to prove levitation erroneous).

This game was awful, and worse, it was in a USCF tournament, if I would have won, I would have tied for 1st.

DON'T EVER PLAY DRUNK! This is one of my most painful loses. I choose to play my favorite opening, so I was very excited from the beginning. After my opponent's wrong exchange -a rook for a knight- he was playing one move every three days in the end of his time, probably to break my nerves. Before the move 63 I was thinking all the time saying to my self: "You have to take his last pawn with your rook and after you'll succeed to promote one of your two pawns to a Queen. So, you MUST take his last pawn with your rook". Then, something bad happened to me in these days -now I can't remember- and one evening when I was drunk, it was my time to play. And I played 63. g5. I don't love my town as she doesn't love me. I hate them and they hate me. So what?

The ONE loss that really bothered me.
I played in a 1 day tournament on a Saturday, and beat a NM in a knight and pawn ending.
3 days later at chess club, I played a guy rated 500, and lost. Seriously....you cant make this stuff up.
It bothered me so much i came off as rude to him. The next week at the club i apologized to him for my actions. We are good friends now.

This game, played at an OTB tournament back in 2012, when I was 18, legitimately almost made me quit chess. I was rated 1860, which was quite bad, and my opponent (a friendly girl aged 15) playing White was rated 1709. I used to be somewhat talented, but being rated 1860 at 18 was nothing special, and this game definitely made me realize that I would never make it to the top. I'm very satisfied with my 2100 nowadays, though.
Lately they're all losses, unless my opponent runs out of time or shoots themselves in the foot. It doesn't much bother me anymore. I no longer care.