Couple of things for me, had a kick about in Sydney a few years back when it was about 40C and didnt put suncream on or take any liquid with me, after a few hours I soon regretted it, was burnt to a crisp and nearly blacked out at one point.
Another one was training with a semi pro team after taking nearly a year out from football, after getting flogged round the pitch with shuttle runs etc etc I couldnt walk for a week.