Two times come to mind:
When I was first playing, I made a decent bogey to begin the round, on a double water carry par 5. This had me pretty pleased as I couldn't break 100 yet. The second hole had a bunker at 150 out on the right side. I hit a 6i a touch to the right of where I was aiming but it was so well struck it looked to clear it and give me a great angle on my second shot. I was quite happy with this until I started to look for my ball. I looked in the bunker, in the rough, in the fairway, optimistically far from the tee, etc. Pissed, I dropped near the bunker and played the rest of the hole and the round poorly.
My second one was almost disastrous though:
Last week, I was playing a match against my brother who generally putts a bit better than me but is inconsistent with his long game and around the greens. Generally I beat him by 14 strokes or so in stroke play, so i figured if I kept it in play I'd manage fine. I was 2 up through 9 and cruising along by the virtue of solid putting and a few holes of good play overall, though I conceded a couple holes due to bad tee shots. I started to lose control off the tee at about the 11th hole, just as the golf course starts to lengthen insanely. Though I won 10, a par 3 due to a great approach, and was 3 up, I lost on both the par 5s on the back on a pair of hooked tee shots, one knocked down on a tree before it could curve back left, the other in the trees left. I won 15, a short par 3 to stop the bleeding with a timely par, leaving me with 3 holes with a 2 hole lead, but no momentum.
So heading into 16, I decided to play for a safe par with a 7i in the fairway as I normally do, since a partial wedge was a risky play for me that day. I hit first as I'd gained the honor, and decided to play my last brand new prov1x as I did on the last hole. I summoned my focus and I hit a mighty, perfect high draw 190 yards down the left fairway, and it kicked left slightly near the corner of the dogleg right. I knew there was very sparse rough and few trees back there, leaving me with a great angle since I knew my ball would only be out of sight from the tee by a couple yards. I was very pleased with that result, since I knew my brother had to match it to have any hope of winning at all, and if I won the hole I'd almost guarantee winning the match. He hit his ball into the trees at a 45 degree angle, hit a provisional to the same spot, found his original and punched out sitting 2 in the same spot as me. I couldn't find the ball. Not only was I forced to concede the hole, I was only 1 up with 2 to play. I should have been 2 yards off the fairway on the pivotal hole, but instead I needed to win a hole to guarantee the victory.
Warning: Spoiler! (Click to show)
The 17th is a water carry par 3, and I own the par 3s and the water carries because my brother hits a lot of low line drives. My brother, who had the honor, stuck a perfect pitching wedge to 15 feet. I hit a conservative shot due to the uncomfortable yardage and sucker pin, and knowing a tie would be fine. I get a bogey from just off the fringe while he made a great par. All square.
Well, I had one ace up my sleeve: I have never, in 7 or 8 rounds, hit my tee shot on the 18th into the water. My brother on the other hand, does this almost every time we play. And I reminded him of this fact as I informed him he hit first, and needed to win or tie the hole or he'd lose, and I got to pick any club I want based on the result of his shot. The pond is only about 70 yards to carry, but there's a noisy fountain and the hole looks longer than it really is. I pulled out my driver and started waggling it so he could see it and think about it, then let him hit; topped into the water. I quickly switched clubs, as I had no intention whatsoever of hitting driver, walked up to the tee and hit my shot, seeing my opportunity; a perfect 240 yard draw with my 3 iron that almost hit the 150 marker. I played conservatively as I could, getting a bogey while he somehow set up about a 50 foot chip to tie the match. He scared the hole but ran it about 20 feet past and lost the final hole and the match.
Fortunately in the end, the worst possible break didn't cost me the match. However it did make my brother believe in his game a bit more, and his best score is now within 2 strokes of mine. However, I plan on shooting 20 strokes lower than him as soon as possible to restore balance to the universe.