I went running at 1 in the afternoon on a day with 100 degree heat plus humidity that added another 10 degrees, didn't have any water, and for some idiot reason decided to run hills. I jogged a mile through the park down to the hill, did 5 repeats at increasingly slower and slower speed until it became obvious it was too hot to run, and then on the way back up literally had to stop and lie down in the woods for like 20 minutes before I could make it the rest of the way back. Then the stupidest part is I go back to the car, and felt like I hadn't worked out probably so made the absolutely lunatic decision to run a couple of more miles, got about a K in and had to stop and literally collapsed. I had to more or less crawl back to the car.
The worst time I ever hit the wall was when I was injured on vacation and went biking, and really had no idea of what my limits were, so I was biking up this mountain and felt really good, reached my planned spot and felt great so decided to keep going to the beach, made it to the beach, felt great, turned around to go back up the mountain and at this point it was hot, midmorning and I hadn't thought to bring any food or water, and I hit the wall so hard. Had to sit in the road for an hour until I got the energy to push the bike back up the mountain and had to call for a ride back.
Both were due to pure stupidity really.