I recently played in a 3-day tournament and came in second place after a pretty brutal final round (5 hours in the pouring rain with poor play by me). I lost by one stroke to someone who I know did not shoot the scores that were posted.
During the second day he had a blowup hole of a 10 on a par 4 (with a decent round otherwise) where he signed for a 9 instead of the 10 he should have carded. I knew the mistake was there, but I didn't want to sort of rub salt in the wound of it already being bad enough since I was ahead of him by 3 and tied for the lead. This was likely a mistake on my part to let it happen in the first place. In addition to that, I had to repeatedly (~5-7 times) ask him and his caddy (who was his girlfriend) to be quiet during both mine and our playing partner's swings due to their loud conversation. There were also three times before I started asking them to be quiet where they would talk as I would about to swing so I would step back and look at them until they stopped.
Regardless, the third day comes up and it's terrible weather. It's raining with probably around 5% of the course having stagnant standing water. The decision is made that we will play anyways, so we go out and play another 18. During this round there is lift clean and place in effect through the green, which means that anywhere in the rough, fringe, or fairway you can mark your ball, clean it, and place it anywhere within one clublength no nearer the hole. One time while I was near this player he was going to place it in a spot nearer the green, so I merely made a friendly reminder that he wasn't allowed to do that ("Hey, just a heads up that your placement of the ball can't be any nearer the green, the same as if you were dropping from a hazard."). I did, however, observe from a distance while he did exactly that on at least three occasions because going closer meant he could place at a more beneficial angle around a tree or for a chip. Since I wasn't near him I did not say anything just because, while it appeared obvious to me, there was the possibility that distance distorted my view of his placement. One of those three placements included an improper distance from his placement, where he used his driver (which was fine) but placed it a good 6" beyond the end of the driver to get the better angle around the tree.
The drops were minor things to me, at least in comparison to what irked me the most about this person's behavior on the final day. Were were paired in a group of four with me and one other tied for the lead, one person one stroke behind, and this individual three strokes behind. Throughout the day both he and his caddy appeared to make a point of talking while others were swinging. I know it cost me at least two strokes on one hole with OB left where his caddy (still his girlfriend) burst out laughing in the start of my downswing (apparently he said something funny) and my attempt to abort the swing resulted in the ball hitting the toe of the club and duck hooking OB. It wasn't one of those polite "ha ha, that was mildly funny" laughs but a "I just about choked I laughed so hard" laugh which is the only reason I tried to stop the swing (it startled me to be honest when the only other noise had been the rain before it). After this they stopped from talking while people were teeing off, but they apparently figured that you couldn't hear them making out or talking noisily just because you were 15' away in the fairway. On the greens there were a couple incidents where the caddy yelled across the green to ask for a score from a player in the middle of someone's putting stroke, but that can just be chalked down to the fact that I imagine this was her first couple times ever on a golf course.
I was quite disappointed when we turned in the scorecards and I found that he beat me by one stroke, but at that point I knew it would just be petty to mention the mistake on the previous day's scorecard ("Hey mister, I'm not a sore loser or anything but this guy cheated."). I'm conflicted about how I feel since I did play poorly on the final round while he played well, but I also know that he at the very least was not a very scrupulous competitor. There were money payouts (he received ~$100 to my $45) but I am mostly let down by the fact that I feel I should have won if I had spoken up instead of remained quiet. At the same time I'm not sure how sportsmanlike it would have been to point out his mistakes or ask for the tournament organizer to talk to his caddy about golf etiquette after the second round (he had a much more well versed caddy the first day) since it would have felt like either kicking him while he was down or punishing someone who was partially being instigated by the player.
How would you have handled this situation or something similar?