(Just posted something to this effect on the Nomeansno discussion forum. Perhaps I should sue myself for plagiarism?)
I got to thinkin'... some time ago, I knew a Native American "spiritual teacher." (I don't want to call him a "medicine man" because I don't know if I'd be using the term correctly, frankly. He was a pipe-carrier and described himself as heyoka). He claimed that drinking cold water on a hot day actually affected the body temperature such that it had the ultimate effect of making you hotter. To help you feel cooler, he said, you should drink hot water on a hot day. (I'm pretty sure I've encountered this in popular culture somewhere, as well, though I forget).
Unwinding at home, I find this thread on the internet answering the question from a western medical point of view:
I am personally drinking cold water in today's heat, but for some time, I tried to take his advice. I begin to suspect he was wrong, as the reply to the above thread suggests.
I'd be curious if anyone else has encountered this notion.