It is common in advanced billiards for the opponent to concede an easy winning shot - especially if the previous shots (to get to that shot) were incredible, such as in the video. There was no chance that Efron was going to miss that 9 ball. He probably hasn’t missed that easy of a shot since he was a beginner. It just doesn’t happen.
A new one on me - made me laugh a lot, thanks!
British GM Tony Miles once played in a strong tournament while lying down. See (https://xpertchesslessons.wordpress.com/2020/02/12/vlastimil-hort-remembers-tony-miles/) for part of the story.
This is pretty much dead at international level now because of Hawkeye - video replays. In fact, a batsman is now allowed to ask the off-field umpires to check the replays if he’s given out, which would have been unheard of a decade or two back.
Cricketers do shake hands on a draw, and once in 2001 Alec Stewart conceded an ODI game at Headingly against Pakistan after the crowd invaded the pitch with Pak still needing a couple to win.
This isn’t uncommon. I often stand at my chair for a bit after a bathroom break or a walk around the room. There is one player, though, at my local club that gets up and down non-stop – sit stand sit stand sit stand – and I know some players find it distracting.
Fabiano Caruana had a post-game interview once where he said something like, “I thought my position was fine and that I had equalized as black, but when I got up from the board I saw the position on the TV monitors from white’s perspective, and it was immediately clear to me that I was in terrible shape.”
If you were playing a series of five minute games with people in the park or at some sort of event…and you wern’t too busy, and someone approached you and said “I’d like to play you, but no timers. A ‘gentlemens game’”
Would you be insulted? Decline?
I ask, because while I enjoy the personalities Twitch streaming from parks and such…I’ll never be able to play a five minute game. I wouldn’t even be happy with 10. Now I’m sure I’ll never run into Levy Rozman or Anna Cramling playing in a park, I’m curious how the average highly rated player would react.
Interesting thread. So it’s against the rules to react to a bad move during the match. What about after? Game’s over, you’ve shaken hands with your opponent and reset the board; is it considered crass to say, “I can’t believe I made that bonehead move with my knight!”, or mutter to yourself that it’s time to give up on chess and take up Candyland, instead?
Generally, it is considered good manners to analyze the game with your opponent afterwards. If there are still other games going on, usually you step outside the tournament hall and find someplace to set up, so you don’t disturb others.
Or, instead, you can stand on top of the table and shout “Why must I lose to this idiot!” 
Chess clearly needs more of this energy.
Well this has never happened to me in 50 years of playing.
If he’s just standing behind his chair, I don’t see any objection.
Me too!
The main problem is that the game might take a long time.
I say, old boy - we highly rated players are not ‘average’! 
I ran school chess teams for years - and we played in adult leagues too.
I told all my players that I’d like them to do their best, but that the most important thing was to win / lose gracefully.
No showing off and no whinging. They were to shake hands after every game and say “Thank you.”
If they had blundered horribly, they could then leave the building and quietly express their frustration well away from the board!
Although we had some very strong sides (and we won National events), I was proudest when the League Secretary told me “Your players are the best-behaved children we’ve ever seen. They are welcome at every club in the League.”
Funnily, I only tilt when I blunder to a bot.
In the first round of a British Chess Championship, two of my good friends were paired together. Andrew was an International Master, whilst Ron was rated in the top 100 in England.
Whilst the usual boring introductory speeches were going on, Ron quietly took hold of the board on his side and slowly lifted it. 
To avoid all the pieces sliding into his lap, Andrew grasped his side of the board and lifted it to balance things.
Ron now lifted the board a bit more - so did Andrew.
Now Ron slowly stood up and kept lifting the board. 
By now Andrew was committed - and also stood up.
Nearby players were now starting to laugh … and the speaker was looking around to see why players weren’t listening to him.
Fortunately Ron now slowly reversed the process and gradually sat down and lowered the board (Andrew following suit.)
Afterwards Ron said he had intended to climb onto the table and keep lifting 
, but changed his mind as he thought he would be disqualified!
I guess if you’re not Nimzovich, you need to be careful…