Late SAFD: I have two that come to mind:
2. The craziest/scariest I ever had was Lake Placid Ironman in 2014. This is a long one haha. There was a thunderstorm closing in at the start, but the race announcers said we are starting as normal but be prepared for the swim to get cut short. It was a two loop swim, where you had to get out of the water after the first loop and run back over to the start a few hundred meters away. I finished the first loop and it was already raining and I could hear thunder and see lightening. Looked around at the race officials expecting them to say don't do another loop, but nope no one stopped me. That second loop was terrifying. The water was so cold my hands were getting shooting pains and I thought maybe lightening was striking the water and I was being slightly electrocuted (race brain). Luckily I'm a fairly strong swimmer and finished my second loop and ran to the transition tent. I fully changed clothes between the swim and the bike because I "wanted to start the bike dry" which went out the window as it was pouring, but as I was in the tent I heard a volunteer say "they're all coming". Turns out they sounded an alarm and told everyone still in the water to swim to the closest shore/dock/anything. People who lived on the lake were pulling athletes onto their private docks and letting them run through their homes to get to the street to run back to transition. I think they waited so long because of age group qualifiers to Kona and didn't know what to do. The bike was still pouring rain and the hills at Lake Placid are crazy which was a terrifying combo. I was riding my breaks so hard on all the downhills out of fear of skidding out and losing all the momentum for the up hills. Lighting was striking uncomfortably close to the course (at least for me but was given no notice to shelter) The bike was also two loops and by the second loop the sun came out and I, of course, got sunburnt because who puts on sunscreen when they've just been destroyed by a multi-hour-long thunderstorm. The run was also two loops- consistency haha. The second loop it had gotten dark and and temperatures plummeted. Some random angel runner gave me a pair of unopened fleece sleeves which saved me. I survived but it was a long 15+ hour day hahaha