I've witnessed some bad sportsmanship at tournaments; however they had nothing to do with chess.
Really Bad Sportsmanship in Real Tournaments

speaking of tal,the best players in chess history used some evil tricks.why did tal stare at his opponents? to hypnotize them?i dont know if he did it during his whole career but i m sure he stared at his opponents constantly when he was young and in his match with botvinnik.also i know botvinnik didnt trust his seconds at all.on occasions he wouldnot accept analysis from one of his seconds without a signature.a dry ascetic and pedantic man. in his match with bronstien he refused to inform Flohr he had sealed a diferent move and flohr his close friend had analyzed whole night another move which leaded to a win .but only tomorrow when botvinnik was about to resume game while Flohr joyfully was showing him all winning variations suddenly he informed Flohr he had sealed a diferent move and Flohr couldnot restrain himself and burst into tears.also Bronstien constantly used all tricks(bad sportsmanship)in his match with botvinnik.botvinnik himself said he had no relations with petrosian after he had behaved improperly during their match.when i read things happened in karpov korchnoi matches in 1978 and 1981 i feel terrible.also there is no need to talk about fischer behaviors.
karpov and kasparov had their psychological tricks.in old times they used to do all tricks in highest level.even in kramnik topalov match we saw what happened.topalov accused kramnik of cheating.they didnt shake hand and or spoke to eachother and i dont think they still talk to eachother.they avoid meeting eachother dont play at the same tournament.seems like they didnt really care to what we call badsportsmanship nowadays.nowadays that chess is considered a sport and are receiving some attention and look for sponsors to provide financial support,players have started behaving better and show some fairplay.

A guy once accused me of offering draws repeatedly even though i offered him a draw only once.He called the arbiter but fortunately,the arbiter knew me pretty well and believed me when i told him that i only offered a draw once.the game continued and i won,my opponent just left in anger.

I'm not sure wether or not it's rude to eat while playing chess, but I have consistently won every game that I've played while snacking on something

I heard of a player that would shake the table with his knees while his opponent was trying to make a move

A guy once accused me of offering draws repeatedly even though i offered him a draw only once.He called the arbiter but fortunately,the arbiter knew me pretty well and believed me when i told him that i only offered a draw once.the game continued and i won,my opponent just left in anger.
As he was leaving, did you shout "Should have accepted the draw! Did you not hear me offer a draw?"
I probably would have. But then my mouth often gets me into trouble.

A guy once accused me of offering draws repeatedly even though i offered him a draw only once.He called the arbiter but fortunately,the arbiter knew me pretty well and believed me when i told him that i only offered a draw once.the game continued and i won,my opponent just left in anger.
As he was leaving, did you shout "Should have accepted the draw! Did you not hear me offer a draw?"
I probably would have. But then my mouth often gets me into trouble.
The gy looked angry and saying that would have probably gotten me beaten.

I'm not sure wether or not it's rude to eat while playing chess, but I have consistently won every game that I've played while snacking on something
In the good old days, everybody smoked. In the chess club I went to as a boy, most of the players smoked pipes. Sometimes you could barely see the board.

A guy once accused me of offering draws repeatedly even though i offered him a draw only once.He called the arbiter but fortunately,the arbiter knew me pretty well and believed me when i told him that i only offered a draw once.the game continued and i won,my opponent just left in anger.
As he was leaving, did you shout "Should have accepted the draw! Did you not hear me offer a draw?"
I probably would have. But then my mouth often gets me into trouble.
The gy looked angry and saying that would have probably gotten me beaten.
If he threatened you, you could have said "I hope you're better at fighting than you are at chess!"
Thinking about it, it's surprising I don't get beaten up every day.

Do y'all think drinking alcohol while playing is bad? I was always polite and all when I drank. I'm sure my opponents could smell it. I would just take a McDonalds cup or BK or whatever and put beer (sometimes something stronger) in it and put the lid and straw back. It only helped my opponent. If my opplnents now were to drink it wouldnt bother me at all. Its not smoking. I dont do that anymore. My rating did demonstrate a different level of playing ability.

A guy once accused me of offering draws repeatedly even though i offered him a draw only once.He called the arbiter but fortunately,the arbiter knew me pretty well and believed me when i told him that i only offered a draw once.the game continued and i won,my opponent just left in anger.
As he was leaving, did you shout "Should have accepted the draw! Did you not hear me offer a draw?"
I probably would have. But then my mouth often gets me into trouble.
The gy looked angry and saying that would have probably gotten me beaten.
If he threatened you, you could have said "I hope you're better at fighting than you are at chess!"
Thinking about it, it's surprising I don't get beaten up every day.
He was a lot older and bulkier than me.

The worse I've ever met myself in a tournament is a guy who had a losing position, and instead of resigning properly, just stood up and said "that's enough" before leaving. No shaking hands, no "nice game" or anything of that kind, and above all no help to put back the pieces in place and reset the clocks or give the results to the TD.
Not exactly a terrible thing.
When I played team matches for my old club, it happened once that one of the players of my team suffered from an opponent who started kicking him under the table when he got into a better position. The guy denied it of course when the TD was called, so nothing happened. Our player just backed his chair one meter behind the table - he had to stand up to play his moves but anyways he won pretty fast after the incident.

The worse I've ever met myself in a tournament is a guy who had a losing position, and instead of resigning properly, just stood up and said "that's enough" before leaving. No shaking hands, no "nice game" or anything of that kind, and above all no help to put back the pieces in place and reset the clocks or give the results to the TD.
Not exactly a terrible thing.
When I played team matches for my old club, it happened once that one of the players of my team suffered from an opponent who started kicking him under the table when he got into a better position. The guy denied it of course when the TD was called, so nothing happened. Our player just backed his chair one meter behind the table - he had to stand up to play his moves but anyways he won pretty fast after the incident.
The first incident you mentioned has happend a lot of times with me too.Players just take off,without signing the scoresheet,no setting their pieces,no shake hands,with a look of disgust on their face.This is pretty common and has happend a lot of times with me before.

Irontiger,
"Quel jouer gauche!" (Did I even say that right?) What I meant was, "What a classless player!" In my opinion, he should have been reprimanded by the TD at least, or removed from the tournament at most. Even most really young players, like under ten, know not to do that kind of crap!

In our clubs tournament that we had a few weeks ago there is a 16 year old kid that's really good but he has the worst ego after he beat a kid that was 4 years younger then him he told him "good try but you never stood a chance" the 12 year old did not feel like playing anymore especially after the 16 year old won the tournament.
This is a game I observed between to expert-level players. Black had an extra passed pawn in an endgame with a Queen on each side. Both colors had three kingside pawns, the only pawn advanced was Black's g6-pawn, because he had fianchettoed his Bishop, Black also had a pawn on the b5 saquare. Black, setting up his Queen to prevent a draw by three fold repetition in the event White tries to take advantage of the bank rank and a1-h8 diagnol, thought his game was quite simply won. White, desperate, checked the opponent's King, to which Black responded by moving his King out of check, much to my horror. White had purposely checked the King, but also had the Queens connect in the check, Black could have taken White's checking Queen for free, but missed it because he wasn't expecting it. White, to Black's horror, then responded by taking the opposing Queen for free, winning the game. Black responded by just letting his time run out.