Mouse-slips are a part of online chess. Beat 'em and deny the rematch.
Mouse Slip - how to react?

My question to the greater chess community is, what is the proper etiquette if your opponent has a "mouse slip". I recently played a game where my opponent made a bad move and claimed he had a mouse slip. I would have let it pass but he accused me of taking advantage of him. I considered his behavior petty and ungentlemanly but it begged a bigger question. What is the proper thing to do? There must be a rule in regular chess if a player drops his piece, etc.
Yours truely, Hardboiledeggs
Take the piece and don't think twice, except for tactical reasons. Most likely he would do the same to you. No random CC user is worth the benefit of the doubt. I do not think anybody has ever shown me grace after a mouse slip and I never ask.

This is a 9 year old post why are people commenting on this.
Explain your logic for why people wouldn't comment on this because of its age? This kind of statement never makes sense to me, and I'd like someone to explain why they ask this.

I'm surprised at all the people in this thread who feel that not only does etiquette not dictate that one should give a draw to an opponent whose mouse slipped, but it's poor form to even ask for one! My view is very different. Mouse slips happen to just about everyone; yes, to some minor degree it's a player's "fault" for letting his finger on the mouse button, but only in the same sense as it's someone's fault when he stubs his toe. I'm sure most of you don't go around telling people, "You deserved it" in that situation!
More to the point, mouse slips aren't a fundamental part of the game of chess, just an unfortunate side effect of the user interfaces we use to play it online. And, really, who would want it to be part of chess? If you were designing a way to play chess and you had the ability to make mouse slips easy or impossible, surely you would choose to make them impossible. After all, they don't enhance the game experience in any way. Of course they're frustrating to the victim, but even for the side benefiting from the slip, I think many people find it less than satisfying to be handed an unearned win that way.
If there were a way to know for certain when a mouse slip has occurred, and to ignore that input, I can't see that there would be any downside to doing so. Of course, in real life, there are complicating factors, including that on chess.com, there's no way to mitigate a game-affecting mouse slip other than offering a draw (or resigning), which you presumably were not ready to do if you were still playing the game; that it's often difficult to know whether a move was a mouse slip or a mistake; and that if called on to be the magnanimous side, you don't have any way of knowing whether your opponent would have made the same gesture had it happened to you.
With all that said, in a situation where a) something is clearly a mouse slip (as in the example of the Rook stopping one square short of a capture, or even any senseless move on the part of a piece that had a sensible move available), and b) you do not believe you had great winning chances before the slip occurred, I feel somewhat strongly that the sportsmanlike thing to do is to offer the draw. I will offer it myself in such a situation, and I will request it when I'm on the losing side of the slip, albeit without a strong expectation that my opponent will be a good sport and accept.

I'm surprised at all the people in this thread who feel that not only does etiquette not dictate that one should give a draw to an opponent whose mouse slipped, but it's poor form to even ask for one! My view is very different. Mouse slips happen to just about everyone; yes, to some minor degree it's a player's "fault" for letting his finger on the mouse button, but only in the same sense as it's someone's fault when he stubs his toe. I'm sure most of you don't go around telling people, "You deserved it" in that situation!
More to the point, mouse slips aren't a fundamental part of the game of chess, just an unfortunate side effect of the user interfaces we use to play it online. And, really, who would want it to be part of chess? If you were designing a way to play chess and you had the ability to make mouse slips easy or impossible, surely you would choose to make them impossible. After all, they don't enhance the game experience in any way. Of course they're frustrating to the victim, but even for the side benefiting from the slip, I think many people find it less than satisfying to be handed an unearned win that way.
If there were a way to know for certain when a mouse slip has occurred, and to ignore that input, I can't see that there would be any downside to doing so. Of course, in real life, there are complicating factors, including that on chess.com, there's no way to mitigate a game-affecting mouse slip other than offering a draw (or resigning), which you presumably were not ready to do if you were still playing the game; that it's often difficult to know whether a move was a mouse slip or a mistake; and that if called on to be the magnanimous side, you don't have any way of knowing whether your opponent would have made the same gesture had it happened to you.
With all that said, in a situation where a) something is clearly a mouse slip (as in the example of the Rook stopping one square short of a capture, or even any senseless move on the part of a piece that had a sensible move available), and b) you do not believe you had great winning chances before the slip occurred, I feel somewhat strongly that the sportsmanlike thing to do is to offer the draw. I will offer it myself in such a situation, and I will request it when I'm on the losing side of the slip, albeit without a strong expectation that my opponent will be a good sport and accept.
The problem with etiquette is it is all just opinion. I prefer to simply go by the rules of the game as they are fixed, without debate.
Of course it is unfortunate when someone mouse-slips and if there were a completely fail-safe way to determine that a move was a mouse-slip then the system could take back the move, with a time-penalty, but obviously that will never be the case. If I'm playing a friend or someone I know then I may react differently, but I'm talking about random opponent games here.
If I mouse slip though I take full responsibility for it, it's my fault and I deserve to lose the game, if it was a bad enough mouse slip that that is the outcome. I don't need an opponent to offer me a draw. Ultimately it was my incompetence that caused it, in the same way that in over the board chess if I accidentally touch a piece on my way to the piece I meant to move then I would have to move that first piece. There are pros and cons with online chess. You can touch as many pieces as you want and still move a different one at the end of it, but on the downside, yes you have mouse slips.
Some people have a lot more mouse-slips than others though so it isn't just pure luck. I don't really remember all that many mouse-slips in my games, though I do it in puzzle-rush far too often. And it's always totally my fault.
I can only tell you about myself:
1. If I make a critical mouse-slip, I resign without comment.
2. If my opponent makes what I suspect to be a mouse-slip, I take that piece, quick as a flash. Any moaning = no replay.
Chess is not a "second chance" game, all moves are final.
So cringe

computer mice slip, whether being "hastey" or not. chesshere.com used to have a "confirm move" check box where you had to confirm every move. if I ran a site, I would have enable an ability like this. but for this site with no such feature, take the piece and dont fret about it.
Well if you ever come back from you 8 year chess hiatus then I have good news! Chess.com has a confirm move feature now! Lol

If it's a very obvious mouse slip (not all blunders are mouse slips) then I'll give a takeback.
But if the website doesn't allow takebacks then too bad, better luck next game.
If I make a big blunder then I'll just resign and move on to the next game.

The problem with a draw is it affects the ratings... it's not an abort.
If someone rated lower than me mouse slips their queen, and I give them a draw, I lose rating points... that's a silly outcome. That's why I normally wouldn't give a draw, but would happily give a takeback for an obvious mouseslip.

Oh, that also makes a difference for me... if I'm winning / outplaying them all game long, and they mouseslip, then I usually wont give a takeback or draw or anything. They should have some dignity and just resign
And of course, I don't have a double standard. I would immediately resign in their position. No hard feelings, and I'd try to do better next game.
They have mouse slips, cats pajamas, and other such things at the Thrift shop!