There is a joke which may be a possible origin: A man was about to fly out to spend a year abroad, and before he left his wife said to him, "You'll be away so long, so if your 'biological needs' get too much, I'm alright with you finding someone to help you handle them."
關於「炒飯」，有個笑話。有個男人要出國一年，臨走前，老婆對他說，出門在外這麼久，若有生理需要，可以找人解決。