I've been showing since I was 3 and am now 30-something. I've been to probably hundreds of shows, both small local open shows and big national-level breed shows. Of course there have been countless embarrassing moments! Life happens :)
-I was putting in a killer western pleasure ride on my youth mare. I had a soft hold on my split reins, completely relaxed... and dropped my left rein. While loping. In an open-level class. The judge wasn't looking, so I said whoa, grabbed her headstall by the cheek, pulled her head around so I could grab the rein, and loped off again. We ended up 2nd!
-same show, same class the next year. New fancy show headstall on the same mare. I'd only used it a handful of times, and didn't realized that the leather had stretched out just a tad. We were standing in the line-up, the judge had just turned in his card and was standing in front of me talking to another exhibitor when my mare gave a great big full-body shake--and her headstall flew off! The judge was doubled over laughing at me while I got off to put her headstall back on.
-we attend our local county fair every year, and it's always my favorite! We used to have a society show, which had everything from draft horses to hackney roadster ponies and saddlebreds. I took the same paint mare in the open english pleasure (mind you, this mare had been hauled over many states and I showed her in every class imaginable) which included quarter horses, saddlebreds, arabians, TB's, etc. A big saddlebred came along the inside to pass and my mare decided to give a great saddle bronc demonstration in from of my hometown crowd! I stayed on somehow, but spent the remainder of the class bending and flexing in lots of small circles in the middle of the arena while the class finished.
-we were attending a large AQHA/APHA combined circuit so the crowd was fairly big (meaning EVERYONE and their brother got to witness this). My very seasoned, well-trained pleasure horse decided that she was absolutely petrified of the judge wearing the dark green trench coat. Every time we went down the arena wall toward that end of the arena, her head came up, ears forward, nostrils flaring, tense, and eyes on that scary woman!!! In the line-up, the judge came over to pet my horse and talk to her and the stupid mare practically tripped over herself running backward. I never had a problem like that before or since. Who knows!
-Showing in amateur horsemanship for the first time since graduating out of youth. It was a big show with several very talented and experienced riders. The pattern was very very long and involved, and I was the last to go. I totally thought I nailed it and was so proud of my horse! I lined up with everyone else waiting for the placings, and one of the judges walked up to me and said "you know, you'd have won it under all 4 of us if you'd remembered to back up at the end".
-My first real show horse was a 16.1 hand gelding who was a big puppy dog. I was about 10 and very small for my age. I got the bright idea that I wanted to show in trail, so my dad helped me practice for weeks so I could show in 13/U trail at the state fair. I got all the way through the pattern and the last obstacle was getting off your horse, ground-tying, walking a circle around him, and then re-mounting. I couldn't get back on by myself without a big mounting block!!! I tried climbing up my stirrup and fender, but it just didn't work :) I was DQ'ed of course, and they no longer require a dismount in trail. I have anotherr 16.1 hand gelding and even though I'm at least a foot taller, mounting can still be awkward at best when you're in heavy chaps.
Those are just the doozies that really stand out--there have been a lot of other moments, but life goes on :) I now mainly show young horses to get a solid foundation on them. The babies are really good at doing silly things at inopportune times!